Error 554 5.4.14: Hop Count Exceeded - Fix Guide 2025

Delivery has failed to these recipients or groups:

user@external-domain.com

The maximum hop count was exceeded for the message. This usually
indicates a mail loop between servers or an incorrect mail routing
configuration.

Diagnostic information for administrators:
Generating server: mail.company.com

#554 5.4.14 Hop count exceeded - possible mail loop ##5.4.14 Hop count exceeded - possible mail loop ##

# Identify the problematic connector
Get-SendConnector | Format-List Name,AddressSpaces,SmartHosts

# Remove accepted domain from send connector (if incorrectly included)
# First, get current address spaces
$connector = Get-SendConnector "Internet Connector"
$connector.AddressSpaces

# Set correct address space (route to internet, not to yourself)
# Option 1: Route all external mail via smart host
Set-SendConnector "Internet Connector" -AddressSpaces "SMTP:*;1" -SmartHosts "smtp.emailprovider.com"

# Option 2: Use DNS for external routing (no smart host)
Set-SendConnector "Internet Connector" -AddressSpaces "SMTP:*;1" -DNSRoutingEnabled $true -SmartHosts $null

# Verify change
Get-SendConnector "Internet Connector" | Format-List Name,AddressSpaces,SmartHosts,DNSRoutingEnabled

# Check current smart host
Get-SendConnector | Format-List Name,SmartHosts

# Verify smart host doesn't resolve back to Exchange
$smartHost = "smtp.relay.com"
Resolve-DnsName $smartHost

# If smart host was pointing to Exchange, fix it
Set-SendConnector "Outbound to Internet" -SmartHosts "correct-relay.emailprovider.com"

# Or remove smart host and use DNS
Set-SendConnector "Outbound to Internet" -SmartHosts $null -DNSRoutingEnabled $true

# Test the fix
Send-MailMessage -From "test@company.com" -To "test@external.com" -Subject "Loop Test" -SmtpServer localhost

# Check hybrid send connectors
Get-SendConnector | Where-Object {$_.Name -like "*O365*" -or $_.Name -like "*Microsoft 365*"} |
    Format-List Name,AddressSpaces,SmartHosts

# Check inbound connector from O365
Get-InboundConnector | Format-List Name,SenderDomains,TlsSenderCertificateName

# Verify connectors don't create loop
# Outbound to O365 should route cloud domains
# Inbound from O365 should route on-prem domains only

# Re-run Hybrid Configuration Wizard if needed
# This reconfigures connectors correctly

# Find the forwarding loop
# User A forwards to User B, User B forwards to User A

# Disable forwarding on one mailbox to break the loop
Set-Mailbox "UserA" -ForwardingAddress $null -ForwardingSmtpAddress $null

# Or remove the problematic inbox rule
Get-InboxRule -Mailbox "UserA" | Where-Object {$_.ForwardTo -ne $null} | Disable-InboxRule

# To prevent future loops, disable forwarding to external addresses
Set-RemoteDomain Default -AutoForwardEnabled $false

# If spam filter or gateway is causing the loop:
# 1. Check MX records point to correct gateway
Resolve-DnsName -Name company.com -Type MX

# 2. Verify gateway forwards to correct Exchange server
# Check gateway configuration (vendor-specific)

# 3. Ensure Exchange doesn't route back to gateway for internal mail
Get-TransportConfig | Format-List InternalSMTPServers

# 4. Add gateway to internal servers if needed
Set-TransportConfig -InternalSMTPServers @{Add="10.0.0.50"0.0.50"}  # Gateway IP

# 1. Test mail flow to previously failing destination
Test-Mailflow -TargetEmailAddress "user@external-domain.com"

# 2. Send test message and verify delivery
Send-MailMessage -From "admin@company.com" -To "test@external-domain.com" -Subject "Loop Fix Test" -Body "Testing mail flow after loop fix" -SmtpServer localhost

# 3. Check message tracking for successful delivery
Get-MessageTrackingLog -Start (Get-Date).AddMinutes(-10) -Sender "admin@company.com" |
    Format-Table Timestamp,EventId,Source,Recipients,RecipientStatus

# 4. Monitor for new 554 5.4.14 errors554 5.4.14 errors
Get-MessageTrackingLog -Start (Get-Date).AddHours(-1) -EventId "FAIL" |
    Where-Object {$_.RecipientStatus -like "*5.4.14*"4.14*"} | Measure-Object

# 5. Check transport queues are draining
Get-Queue | Format-Table Identity,Status,MessageCount

# Before changing connectors, test mail flow
Test-Mailflow -TargetEmailAddress "user@external-domain.com"

# Document current configuration
Get-SendConnector | Export-Csv "SendConnectors_Backup.csv"
Get-ReceiveConnector | Export-Csv "ReceiveConnectors_Backup.csv"

# After changes, immediately test
Send-MailMessage -To "test@external.com" -Subject "Connector Change Test" -SmtpServer localhost