How To Fix Email Service Unavailable Delivery Issues with IPv6 on Amazon Linux

Author: , July 16th, 2021

PROBLEM: Email delivery to Google was failing with a “Service Unavailable” error:

Note that the network address for the destination is shown as IPv6! That is the root cause of the issue: 1. Sendmail is sending mail from the IPv6 address instead of the IPv4 address 2. Google rejects IPv6 senders without proper reverse […]

How To List Running AWS Instances in all Regions Sorted by LaunchTime and Email in a Monospaced Font

Author: , July 1st, 2019

How To Force Sendmail to Process the Mail Queue

Author: , August 4th, 2016

To force sendmail to process the mail queue, execute as root: sendmail -q -v The optional -v enables verbose mode to assist with troubleshooting. To display the current contents of the mail queue, execute as root: mailq

How To Enable Sendmail on CentOS 5

Author: , January 28th, 2011

# vim /etc/sysconfig/sendmail Change: DAEMON=no to DAEMON=yes

How To Setup A Smart Relay Host Port on Sendmail

Author: , January 26th, 2011

Configure the Smart Host Search for DS in /etc/mail/sendmail.cf and edit as follows: Before: DS After: DSyour.mail.relay.yourdomain.com Configure The Port Search for Mrelay and edit as follows: Before: Mrelay, P=[IPC], F=mDFMuXa8, S=EnvFromSMTP/HdrFromSMTP, R=MasqSMTP, E=\r\n, L=2040, T=DNS/RFC822/SMTP, A=TCP $h After: Mrelay, P=[IPC], F=mDFMuXa8, S=EnvFromSMTP/HdrFromSMTP, R=MasqSMTP, E=\r\n, L=2040, T=DNS/RFC822/SMTP, A=TCP $h 2525 Add the following line appropriately […]