Mail messages are stuck in mail queue after changing Outgoing mail IP on Plesk server

Symptoms

• There are multiple IPs on the server. For example: 203.0.113.2 and 203.0.113.111

• Mail messages are sent successfully from 203.0.113.2

• Mail messages are stuck in mail queue after changing Outgoing mail IP to 203.0.113.111 going to Plesk > Tools & Settings > Mail Server Settings > Outgoing mail mode > Send from the specified IP addresses:

  

• There are the following records in /var/log/maillog:

  postfix/smtp[2398]: 674761A0895: to=<[email protected]>, relay=none, delay=688, delays=537/0.02/151/0, dsn=4.4.1, status=deferred (connect to alt4.gmail-smtp-in.l.google.com[173.194.203.26]:25: Connection timed out)
   postfix/smtp[2397]: connect to alt4.gmail-smtp-in.l.google.com[173.194.203.26]:25: Connection timed out

• Checking 203.0.113.111 shows that the IP is not blacklisted

• It is possible to connect to google mail server via 25 port from the old IP  ( 203.0.113.2):

  Note: It might be required to install Ncat package to check the following symptom

  # nc -v -w5 -s  203.0.113.2 173.194.203.26 25
  Ncat: Connected to 173.194.202.26:25.
  220 mx.google.com ESMTP d15si36358376pgi.541 – gsmtp

•  The connection from the new IP ( 203.0.113.111 ) fails with a timeout message:

  Note: It might be required to install Ncat package to check the following symptom

  # nc -v -w5 -s  203.0.113.111 173.194.203.26 25
  Ncat: Connection timed out.

Cause

Network misconfiguration: Outbound connections through port 25 from the selected IP address are blocked on the server.

Resolution

1. Connect to the server via SSH

2. Install Ncat package:

   • CentOS/RedHat/CloudLinux OS:

     # yum install nc

   • Debian/Ubuntu OS:

     # apt-get install netcat

3. Run the following command to check which IP address reaches the external mail server:

   # MAILSERVER=”173.194.203.26“; RE=”[0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3}”; if [[ $MAILSERVER =~ ^${RE}$ ]]; then for IP in `ip a | egrep -o ${RE} | egrep -v 255$|^127|0.0.0.0 | sort | uniq`; do echo -e “nChecking connection: $IP -> $MAILSERVER:25”; nc -z -w5 -s $IP $MAILSERVER 25 &>/dev/null; err=`echo $?`; if [ $err -eq 0 ]; then echo -e “Success: Connection works”; elif [ $err -eq 1 ]; then echo -e “Error: Connection failed”; elif [ $err -eq 127 ]; then echo -e “nError: Install Ncat package”; kill -INT $$; else echo -e “nError: Unexpected error code”; kill -INT $$; fi; done; else echo -e “nError: The value is not an IP address”; fi

   * Where MAILSERVER parameter is the external mail IP address that cannot be reached according to the error logs

4. According to the results from the previous command, apply one of the following solutions:

   • Change the default IP address capable to connect to the external mail servers: Log in to Plesk GUI > Tools & Settings > Mail Server Settings > Outgoing mail mode > Send from the specified IP addresses

   • In case all the IP addresses are not capable to connect to the external mail server, check the server network configuration: Unable to send emails using Plesk local mail server