I have a Debian 10 server which has postfix installed, each time I try to send outbound mail traffic, the server uses IPV6 over IPV4. This causes postfix to log Connection timed out.

I have tried sending packets to google SMTP server using telnet, whenever I run the command telnet gmail-smtp-in.l.google.com 25 the terminal delays for some seconds and then outputs

Trying 2a00:1450:400c:c06::1a...
telnet: Unable to connect to remote host: Connection timed out

Please I have no clue on what is happening.

  • 4
    Using IPv6 over IPv4 is normal and expected. This is how the Internet works. You have a different problem. Most likely your provider has blocked outgoing SMTP. Aug 5 at 19:21
  • @MichaelHampton Thanks so much, I noticed my provider blocks port 25, 465, and 587 by default and I have opened a ticket.
    – Ruby
    Aug 5 at 19:45

Many hosting providers block outgoing SMTP for new customers. There is usually a process by which you can have it unblocked or otherwise send mail; contact the provider for specifics.

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