Troubleshooting Email Delivery in Exchange 2019 / SE Hybrid

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Troubleshooting Email Delivery in Exchange Hybrid

A Complete Guide: Message Trace, Protocol Logs, and Real-World Error Resolution

Exchange 2019 Hybrid | Exchange Online | May 2026

 


1. Understanding the Hybrid Mail Flow Architecture

In an Exchange Hybrid environment, mail flows through multiple components depending on the direction. Understanding this architecture is the foundation of any troubleshooting effort.







 

Direction

Flow Path

Key Components

EXO → On-Prem

EXO → MX/Smarthost → Edge/Mailbox → Recipient

Outbound Connector in EXO, Receive Connector on Edge/Mailbox

On-Prem → EXO

Mailbox → Send Connector → EXO Protection

Send Connector with SmartHost, TLS Certificate

On-Prem → Internet

Mailbox → Send Connector → Internet

Internet Send Connector with DNS Routing

Internet → On-Prem

Internet → MX Record → Edge/Mailbox

MX Record, Receive Connector, Port 25 Forwarding

 

2. Protocol Log — Enabling, Paths, and Reading

2.1 What are Protocol Logs?

Protocol logs record every SMTP conversation between Exchange servers. They capture the full SMTP dialogue including EHLO, STARTTLS, MAIL FROM, RCPT TO, DATA, and response codes. They are the most powerful diagnostic tool available for mail flow issues.

 

2.2 Types of Protocol Logs

Log Type

Server

Path

Purpose

SmtpReceive

Mailbox/Edge

TransportRoles\Logs\FrontEnd\ProtocolLog\SmtpReceive

Inbound SMTP connections

SmtpSend

Mailbox/Edge

TransportRoles\Logs\FrontEnd\ProtocolLog\SmtpSend

Outbound SMTP connections

Hub SmtpReceive

Mailbox

TransportRoles\Logs\Hub\ProtocolLog\SmtpReceive

Internal Hub receive

Hub SmtpSend

Mailbox

TransportRoles\Logs\Hub\ProtocolLog\SmtpSend

Internal Hub send

Edge SmtpReceive

Edge

TransportRoles\Logs\Edge\ProtocolLog\SmtpReceive

Edge inbound

Edge SmtpSend

Edge

TransportRoles\Logs\Edge\ProtocolLog\SmtpSend

Edge outbound

 

2.3 Enabling Protocol Logging

Protocol logging must be enabled on both Receive and Send connectors. By default it is set to None.

 

Enable on Receive Connectors (Mailbox Server):

# Enable on Default Frontend connector

Set-ReceiveConnector 'Default Frontend CMHYBD01' -ProtocolLoggingLevel Verbose

 

# Enable on all receive connectors at once

Get-ReceiveConnector | Set-ReceiveConnector -ProtocolLoggingLevel Verbose

 

# Verify

Get-ReceiveConnector | Select Name, ProtocolLoggingLevel | Format-List

 

Enable on Send Connectors (Mailbox Server):

# Enable on Outbound to Office 365

Set-SendConnector 'Outbound to Office 365' -ProtocolLoggingLevel Verbose

 

# Enable on all send connectors

Get-SendConnector | Set-SendConnector -ProtocolLoggingLevel Verbose

 

# Verify

Get-SendConnector | Select Name, ProtocolLoggingLevel | Format-List

 

Enable on Edge Server:

# On Edge - enable receive connector logging

Set-ReceiveConnector 'Default internal receive connector CMEDGE01' -ProtocolLoggingLevel Verbose

 

# Set log path explicitly

Set-TransportService cmedge01 -ReceiveProtocolLogPath 'C:\Program Files\Microsoft\Exchange Server\V15\TransportRoles\Logs\Edge\ProtocolLog\SmtpReceive'

 

# Restart transport to apply

Restart-Service MSExchangeTransport

 

TIP: Important

Always restart MSExchangeTransport after changing protocol logging settings to ensure the changes take effect immediately.

 

2.4 Finding and Reading Protocol Logs with Tail Command

The -Tail parameter in Get-Content shows only the last N lines of a log file, which is the most efficient way to read large protocol logs in real time.

 

Get the Latest Log File and Read Last 30 Lines:

# Define the log path

$logPath = 'C:\Program Files\Microsoft\Exchange Server\V15\TransportRoles\Logs\FrontEnd\ProtocolLog\SmtpReceive'

 

# Get the most recent log file

$latest = Get-ChildItem $logPath | Sort LastWriteTime -Descending | Select -First 1

 

# Read last 30 lines

Get-Content $latest.FullName -Tail 30

 

# Watch log in REAL TIME (like Linux tail -f)

Get-Content $latest.FullName -Tail 10 -Wait

 

Read Send Protocol Log:

$sendLog = 'C:\Program Files\Microsoft\Exchange Server\V15\TransportRoles\Logs\FrontEnd\ProtocolLog\SmtpSend'

$latest = Get-ChildItem $sendLog | Sort LastWriteTime -Descending | Select -First 1

Get-Content $latest.FullName -Tail 50

 

TIP: Tail Limitation

The -Tail parameter reads from the END of the file. For very large log files, use -Wait to monitor in real time. Note that a new log file is created each hour, so always get the latest file first using Sort LastWriteTime -Descending | Select -First 1.

 

2.5 Understanding Protocol Log Format

Each line in a protocol log contains these fields separated by commas:

 

Field

Description

Example

date-time

UTC timestamp

2026-05-01T06:06:57.291Z

connector-id

Connector handling the session

CMHYBD01\Default Frontend CMHYBD01

session-id

Unique session identifier

08DEA74796A6E2C8

sequence-number

Line number in session

21

local-endpoint

Local IP:Port

192.168.1.4:25

remote-endpoint

Remote IP:Port

40.93.131.26:31611

event

+,-,>,<,*

+ = connected, - = disconnected, > = sent, < = received, * = info

data

SMTP command or response

250 2.6.0 Queued mail for delivery

context

Additional info

TLS negotiation succeeded

 

Reading a Real Session from Our Lab:

# Example of a successful EXO → On-Prem delivery session:

2026-05-01T06:06:57.291Z,...,0,192.168.1.4:25,40.93.131.26:31611,+,,              # EXO connected

2026-05-01T06:06:57.291Z,...,1,...,>,220 cmhybd01... ESMTP MAIL Service ready      # Banner sent

2026-05-01T06:06:57.291Z,...,2,...,<,EHLO PNYPR01CU001.outbound.protection...      # EXO says hello

2026-05-01T06:06:57.291Z,...,3,...,>,250 ... STARTTLS ...                          # We offer TLS

2026-05-01T06:06:57.291Z,...,4,...,<,STARTTLS                                      # EXO starts TLS

2026-05-01T06:06:57.291Z,...,5,...,*,TLS negotiation succeeded                     # TLS established

2026-05-01T06:06:57.291Z,...,22,...,>,250 2.6.0 Queued mail for delivery           # Mail accepted!

 

2.6 Exporting Protocol Logs to CSV

For detailed analysis or sharing with Microsoft support, export protocol logs to CSV format:

 

# Export a specific protocol log to CSV

$logPath = 'C:\Program Files\Microsoft\Exchange Server\V15\TransportRoles\Logs\FrontEnd\ProtocolLog\SmtpReceive'

$latest = Get-ChildItem $logPath | Sort LastWriteTime -Descending | Select -First 1

 

# Import as CSV (skip header lines starting with #)

$log = Get-Content $latest.FullName | Where-Object {$_ -notmatch '^#'} | ConvertFrom-Csv -Header 'DateTime','ConnectorId','SessionId','SequenceNumber','LocalEndpoint','RemoteEndpoint','Event','Data','Context'

 

# Filter for specific session or error

$log | Where-Object {$_.Data -like '*550*' -or $_.Data -like '*fail*'} | Export-Csv 'C:\Logs\smtp_errors.csv' -NoTypeInformation

 

# Export all TLS failures

$log | Where-Object {$_.Context -like '*TLS*' -or $_.Data -like '*454*'} | Export-Csv 'C:\Logs\tls_issues.csv' -NoTypeInformation

 

# Export specific IP session

$log | Where-Object {$_.RemoteEndpoint -like '*40.93.*'} | Export-Csv 'C:\Logs\exo_sessions.csv' -NoTypeInformation

 

 

3. Message Tracking Logs

3.1 What is Message Tracking?

Message tracking logs record every message event as it passes through the Exchange transport pipeline. Unlike protocol logs (which show SMTP conversations), message tracking shows high-level events like RECEIVE, SUBMIT, DELIVER, SEND, FAIL, and REDIRECT.

 

3.2 Message Tracking Event Types

Event

Description

What It Means

RECEIVE

Message received by transport

Mail entered the transport pipeline

SUBMIT

Message submitted to transport

Mail submitted from mailbox store

DELIVER

Message delivered to mailbox

Mail successfully delivered

SEND

Message sent to next hop

Mail handed off to next server

FAIL

Delivery failed

Mail could not be delivered

REDIRECT

Message redirected

Mail redirected by rule or policy

RESOLVE

Recipient resolved

Recipient address resolved in AD

EXPAND

Distribution group expanded

DL membership expanded

DEFER

Delivery deferred

Temporary delivery failure, will retry

DROP

Message dropped

Mail dropped by policy or filter

 

3.3 Message Tracking Commands

Basic Message Tracking:

# Get all events in last 30 minutes

Get-MessageTrackingLog -Start (Get-Date).AddMinutes(-30) | Select Timestamp, EventId, Source, MessageSubject, RecipientAddress | Format-List

 

# Filter by specific event type

Get-MessageTrackingLog -Start (Get-Date).AddMinutes(-30) -EventId DELIVER | Select Timestamp, MessageSubject, RecipientAddress | Format-List

 

# Find failed messages

Get-MessageTrackingLog -Start (Get-Date).AddHours(-2) -EventId FAIL | Select Timestamp, MessageSubject, RecipientAddress, RecipientStatus | Format-List

 

# Search by subject

Get-MessageTrackingLog -MessageSubject 'Test Email' -Start (Get-Date).AddHours(-1) | Format-List

 

# Search by sender

Get-MessageTrackingLog -Sender 'user@domain.com' -Start (Get-Date).AddHours(-1) | Format-List

 

# Search by recipient

Get-MessageTrackingLog -Recipients 'user@domain.com' -Start (Get-Date).AddHours(-1) | Format-List

 

Export Message Tracking to CSV:

# Export last 24 hours of failed deliveries to CSV

Get-MessageTrackingLog -Start (Get-Date).AddHours(-24) -EventId FAIL | Select Timestamp, EventId, Source, MessageSubject, SenderAddress, RecipientAddress, RecipientStatus | Export-Csv 'C:\Logs\failed_deliveries.csv' -NoTypeInformation

 

# Export all events for a specific sender

Get-MessageTrackingLog -Sender 'raghu@cloudmonkeys.xyz' -Start (Get-Date).AddDays(-1) | Export-Csv 'C:\Logs\sender_trace.csv' -NoTypeInformation

 

# Quick summary of mail flow

Get-MessageTrackingLog -Start (Get-Date).AddHours(-1) | Group-Object EventId | Select Name, Count | Sort Count -Descending

 

3.4 Exchange Online Message Trace

In Exchange Online, use Get-MessageTrace or the EAC Message Trace tool to trace mail flow within EXO.

 

# Connect to Exchange Online

Connect-ExchangeOnline -UserPrincipalName admin@cloudmonkeys.xyz

 

# Basic message trace

Get-MessageTrace -SenderAddress 'raghu@cloudmonkeys.xyz' -StartDate (Get-Date).AddHours(-2) | Format-List Subject, Status, ToAddress, Received

 

# Trace by recipient

Get-MessageTrace -RecipientAddress 'ramki@cloudfield.onmicrosoft.com' -StartDate (Get-Date).AddHours(-2) | Format-List

 

# Get detailed trace events

$trace = Get-MessageTrace -SenderAddress 'raghu@cloudmonkeys.xyz' -StartDate (Get-Date).AddHours(-2) | Select -First 1

Get-MessageTraceDetail -MessageTraceId $trace.MessageTraceId -RecipientAddress $trace.RecipientAddress | Format-List

 

# Export to CSV

Get-MessageTrace -StartDate (Get-Date).AddHours(-24) -EndDate (Get-Date) | Export-Csv 'C:\Logs\exo_trace.csv' -NoTypeInformation

 

 

4. Queue Management and Troubleshooting

4.1 Checking Mail Queues

# View all queues

Get-Queue

 

# View queue details

Get-Queue -Identity 'cmhybd01\6' | Format-List *

 

# View messages in a specific queue

Get-Message -Queue 'cmhybd01\6' | Format-List FromAddress, Recipients, Status, LastError

 

# Count messages per queue

Get-Queue | Select Identity, Status, MessageCount, NextHopDomain, LastError | Format-Table

 

4.2 Queue Status Types

Status

Meaning

Action

Active

Messages being delivered

Normal — no action needed

Ready

Queue ready, waiting for messages

Normal

Retry

Temporary failure, will retry

Check LastError for reason

Suspended

Queue manually suspended

Resume with Resume-Queue

Unreachable

No connector found for domain

Check send connector address spaces

 

4.3 Queue Retry and Resubmit Commands

# Retry a specific queue

Retry-Queue -Identity 'cmhybd01\6'

 

# Retry and resubmit (reprocess from scratch)

Retry-Queue -Identity 'cmhybd01\6' -Resubmit $true

 

# Retry all queues

Get-Queue | Retry-Queue

 

# Resume a suspended queue

Resume-Queue -Identity 'cmhybd01\6'

 

# Suspend a queue (stop delivery)

Suspend-Queue -Identity 'cmhybd01\6'

 

# Remove all messages from a queue

Remove-Message -Queue 'cmhybd01\6' -WithNDR $false -Confirm:$false

 

 

5. Real-World Errors Encountered and Resolved

The following section documents every error encountered during a real Exchange 2019 Hybrid lab troubleshooting session, along with the exact fix applied. All errors and fixes are taken directly from live diagnostic sessions.

 

Error 1: Mail Stuck in Drafts — Never Entering Queue

ERROR: Mail never leaves Outlook/OWA — Get-Queue shows Submission with 0 messages

Symptom: Mail sent from on-prem mailbox goes to Sent Items but never appears in transport queue

 

Diagnosis Steps:

Get-Queue

Get-Service MSExchangeTransport, MSExchangeSubmission | Select Name, Status

Get-MailboxDatabase -Status | Select Name, Mounted, Server

FIX: Check and Restart Transport Services

Restart-Service MSExchangeSubmission Restart-Service MSExchangeTransport Verify all MSExchange* services are Running

 

Error 2: EdgeSync LDAP Unavailable

ERROR: Test-EdgeSynchronization -FullCompareMode returns SyncStatus: Failed

FailureDetail: EdgeSync service cannot connect to this subscription because of error 'The LDAP server is unavailable.' CredentialRecords: Number of credentials 0

 

Root Cause: The ADAM (AD LDS) database on the Edge server was corrupt or empty. CredentialRecords showing 0 confirmed the bootstrap credential exchange never completed.

# Verify ADAM is running

Get-Service ADAM_MSExchange | Select Name, Status

 

# Test LDAP port connectivity from Mailbox server

Test-NetConnection -ComputerName cmedge01.cloudmonkeys.xyz -Port 50389

Test-NetConnection -ComputerName cmedge01.cloudmonkeys.xyz -Port 50636

 

# Test ADAM database access

$root = [ADSI]'LDAP://localhost:50389/CN=MSExchangeTransportService,CN=First Organization,...'

$root.PSBase.Children | Select Name, ObjectClass

# Error: 'An operations error occurred' = ADAM database corrupt

FIX: Re-subscribe Edge Server

1. Remove-EdgeSubscription -Identity cmedge01 -Confirm:$false 2. New-EdgeSubscription -FileName 'C:\EdgeSub.xml' -Force (on Edge) 3. Copy XML to Mailbox server 4. New-EdgeSubscription -FileData ([byte[]]$(Get-Content -Path 'C:\EdgeSub.xml' -Encoding Byte -ReadCount 0)) -Site 'Default-First-Site-Name' 5. Start-EdgeSynchronization -Server CMHYBD01

 

Error 3: ADAM Service Fails to Start After Database Deletion

ERROR: EventID 7023: ADAM service terminated with error %%3221225487 (0xC000000F)

The system cannot find the file specified — ADAM database files were deleted but ADAM cannot reinitialize from scratch

FIX: Reinstall ADAM Instance Using Exchange Answer File

1. Run adamuninstall.exe /instancename:MSExchange /unattend 2. Populate AdamInstallAnswer.ini with correct values from registry 3. Run adaminstall.exe /answer:AdamInstallAnswer.ini /quiet 4. If still failing, reinstall Edge Transport role via Setup.exe

 

Error 4: Exchange Setup Fails — Missing Registry Keys

ERROR: Setup Step 6 of 8 fails: The registry key 'SOFTWARE\Microsoft\ExchangeServer\v15\Transport' does not exist

Setup.exe /Mode:Install /Roles:EdgeTransport fails partway through when registry was previously cleaned

FIX: Create Required Registry Keys Before Setup

reg add 'HKLM\SOFTWARE\Microsoft\ExchangeServer\v15\Transport' /f reg add 'HKLM\SOFTWARE\Microsoft\ExchangeServer\v15\Pickup' /f reg add 'HKLM\SOFTWARE\Microsoft\ExchangeServer\v15\Gateway' /f (repeat for all required subkeys)

 

Error 5: ASDat.MSI Installation Fails with Error 1603

ERROR: Installing product ASDat.MSI failed. Fatal error. Error code 1603

Anti-spam MSI package corrupt or broken Windows Installer registration from previous failed install

FIX: Pre-install Hygiene MSIs from Exchange ISO

1. Find MSIs: E:\Setup\ServerRoles\TransportRoles\agents\Hygiene\ 2. Copy ASDat.MSI, ASEntIRS.MSI, ASEntSig.MSI to local path 3. msiexec.exe /i ASDat.MSI ALLUSERS=1 /qn 4. Repeat for ASEntIRS.MSI and ASEntSig.MSI 5. Re-run Exchange setup

 

Error 6: EXO Connector Validation Fails — SubjectMismatch

ERROR: 450 4.4.317 Cannot establish session — SubjectMismatch. Expected: mail.cloudmonkeys.xyz, Presented: CN=cmedge01.cloudmonkeys.xyz

Edge server presenting wrong TLS certificate during EXO connection. Multiple certs with SMTP service causing incorrect cert selection

FIX: Remove Wrong Certs and Set Correct FQDN

1. Remove-ExchangeCertificate for all wrong certs 2. Keep only mail.cloudmonkeys.xyz (Let's Encrypt cert) 3. Enable-ExchangeCertificate -Thumbprint <correct> -Services SMTP -Force 4. Set-ReceiveConnector 'Default internal...' -Fqdn 'mail.cloudmonkeys.xyz' 5. Restart-Service MSExchangeTransport

 

Error 7: PRX2 — DNS Query Failed During Internal Proxy

ERROR: 451 4.7.0 Temporary server error. PRX2 — DNS query failed with error ErrorRetry -> DnsQueryFailed: ErrorRetry

Frontend Transport cannot resolve internal hostname when proxying inbound mail. Caused by multiple DNS servers including public NIC ISP DNS

# Diagnosis

Get-TransportService CMHYBD01 | Select InternalDNSServers, ExternalDNSServers | Format-List

# Found: InternalDNSServers: {202.88.152.10, 202.88.152.8, 192.168.1.11}  <- ISP DNS mixed in!

FIX: Set Explicit Internal and External DNS Servers

Set-TransportService CMHYBD01 -InternalDNSServers '192.168.1.11' -InternalDNSAdapterEnabled $false Set-TransportService CMHYBD01 -ExternalDNSServers '8.8.8.8','8.8.4.4' -ExternalDNSAdapterEnabled $false Set-FrontendTransportService CMHYBD01 -InternalDNSServers '192.168.1.11' -InternalDNSAdapterEnabled $false Set-FrontendTransportService CMHYBD01 -ExternalDNSServers '8.8.8.8','8.8.4.4' -ExternalDNSAdapterEnabled $false

 

Error 8: Mail to EXO Goes to Unreachable Domain Queue

ERROR: A matching connector cannot be found to route the external recipient

Recipients at cloudfield.onmicrosoft.com land in Unreachable queue because no send connector covers that address space

# Diagnosis

Get-Message -Queue cmhybd01\Unreachable | Format-List FromAddress, Recipients, Subject

# Recipients: ramki@cloudfield.onmicrosoft.com — No Matching Connector

 

# Check send connectors

Get-SendConnector | Format-List Name, AddressSpaces

# Found: cloudfield.mail.onmicrosoft.com covered but NOT cloudfield.onmicrosoft.com

FIX: Add Missing Address Space to Send Connector

Set-SendConnector 'Outbound to Office 365' -AddressSpaces 'smtp:cloudmonkeys.xyz;1','smtp:cloudfield.onmicrosoft.com;1' Retry-Queue cmhybd01\Unreachable -Resubmit $true

 

Error 9: 550 5.7.1 Client Host Blocked by Spamhaus

ERROR: 550 5.7.1 Service unavailable, Client host [27.7.57.241] blocked using Spamhaus

Public IP address on Spamhaus PBL (Policy Block List) — common for residential/business ISP IPs

FIX: Request PBL Removal and Use Temporary Workaround

Short term: Set-SendConnector 'Outbound to Office 365' -SmartHosts 'smtp.office365.com' Long term: Request removal at https://www.spamhaus.org/removal/ PBL removal is usually instant for legitimate IPs

 

Error 10: EXO Outbound Connector TLS Certificate Mismatch

ERROR: 454 4.7.5 Certificate validation failure, Reason: SubjectMismatch

Mailbox server presenting certificate that doesn't match the TlsDomain configured on the send connector

# Diagnosis

Get-SendConnector 'Outbound to Office 365' | Format-List TlsDomain, TlsAuthLevel, Fqdn

# TlsDomain: cloudmonkeys.xyz  <- Wrong! Should match EXO cert

FIX: Set Correct TlsDomain and FQDN on Send Connector

Set-SendConnector 'Outbound to Office 365' -TlsAuthLevel DomainValidation -TlsDomain 'mail.protection.outlook.com' -Fqdn 'mail.cloudmonkeys.xyz'

 

 

6. DNS Configuration Best Practices for Hybrid

 

DNS Record

Type

Value

Purpose

cloudmonkeys.xyz

MX

cloudmonkeys-xyz.mail.protection.outlook.com (Priority 0)

Inbound mail routes to EXO

mail.cloudmonkeys.xyz

A

27.7.57.241 (Public IP)

External SMTP endpoint

autodiscover.cloudmonkeys.xyz

A/CNAME

Public IP or autodiscover.outlook.com

Outlook auto-configuration

cmedge01.cloudmonkeys.xyz

A (Internal)

192.168.1.25

Internal resolution of Edge server

cmhybd01.cloudmonkeys.xyz

A (Internal)

192.168.1.13

Internal resolution — do NOT register public NIC

 

Split DNS Configuration (Critical for Hybrid):

# Internal DNS (DC) should resolve servers to INTERNAL IPs

# External DNS (GoDaddy/public) should resolve mail.cloudmonkeys.xyz to PUBLIC IP

 

# Prevent public NIC from registering in DNS

Set-DnsClient -InterfaceAlias 'Pub' -RegisterThisConnectionsAddress $false

ipconfig /registerdns

 

# Set transport to use DC for internal, Google for external

Set-TransportService CMHYBD01 -InternalDNSServers '192.168.1.11' -InternalDNSAdapterEnabled $false

Set-TransportService CMHYBD01 -ExternalDNSServers '8.8.8.8','8.8.4.4' -ExternalDNSAdapterEnabled $false

 

 

7. Quick Reference — Common SMTP Response Codes

Code

Meaning

Common Cause in Hybrid

220

Service ready

Normal — server ready to accept

250

OK / Success

Command accepted successfully

251

User not local — will forward

Recipient in another domain

354

Start mail input

Ready to receive message body

421

Service temporarily unavailable

Server overloaded or maintenance

450

Mailbox unavailable — try again

Temporary failure, will retry

451 4.4.0

DNS query failed

Transport DNS misconfigured

451 4.7.0

PRX2 — Temp server error

Frontend proxy DNS failure

454 4.7.5

Certificate validation failure

TLS cert mismatch or SubjectMismatch

500

Syntax error

Invalid SMTP command

503 5.5.2

Send hello first

EHLO not sent before STARTTLS

504 5.7.4

Unrecognized auth type

AUTH attempted without TLS

550 5.7.1

Rejected — policy

Spamhaus or blacklist block

550 5.7.64

TenantAttribution

EXO connector not matching

554 5.4.14

Hop count exceeded

Mail routing loop

 

 

8. Troubleshooting Checklist

 

When Mail is Stuck in Drafts (On-Prem):

1.     Check all MSExchange* services are Running

2.     Verify mailbox databases are Mounted: Get-MailboxDatabase -Status

3.     Check submission queue: Get-Queue

4.     Restart MSExchangeSubmission and MSExchangeTransport

5.     Check send connector address spaces cover recipient domain

6.     Check external DNS servers are set on transport service

 

When EXO Mail Not Reaching On-Prem:

7.     Verify MX record points to EXO protection

8.     Check port 25 forwarding on router to correct internal IP

9.     Validate EXO Outbound Connector: Validate-OutboundConnector

10.  Check TLS certificate on receive connector matches expected FQDN

11.  Enable protocol logging and check SmtpReceive log for connection attempts

12.  Verify internal DNS resolves hostnames correctly

 

When EdgeSync Fails:

13.  Check ADAM service is running: Get-Service ADAM_MSExchange

14.  Test LDAP ports: Test-NetConnection -Port 50389 and 50636

15.  Run Test-EdgeSynchronization -FullCompareMode

16.  Check CredentialRecords — if 0, re-subscription needed

17.  Verify firewall rules allow ports 50389 and 50636

18.  Check DNS resolution of Edge server FQDN from Mailbox server

 

— End of Document —

Location: Chennai, Tamil Nadu, India

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