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Is it possible to use another port for SMTP connection if 25 port is blocked by ISP?

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George Alibegashvili
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Plesk for Linux kb: how-to ABT: Group B

Applicable to:

  • Plesk for Linux

Question

Is it possible to use another port for SMTP connection if 25 port is blocked by ISP?

Answer

Usually, ISP blocks only outgoing 25 port. There are two options:

  • Contact ISP and ask to unblock 25 port for outgoing traffic.
  • Setup relayhost(smarthost) in postfix following steps from any 3rd-party resource like this.

If ISP also blocks incoming 25 port, it will be impossible to use mail service on this server. Anyway, contact ISP for assistance.

Additional information

  • For configuring Mail Submission port 587 in Plesk for Windows please refer to the article
  • For configuring Mail Submission port 587 in Plesk for Linux please refer to the article

Note: Plesk server cannot be configured to use 587 port for outbound SMTP traffic. Either only 25 or 25 in conjunction with 587 can be used. Also, Plesk will still be listening on 25 port alongside with 587.

Comments

6 comments

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  • Avatar
    Sait Firat NEMIS

    It's is very bad situation. There is no solution ?

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    Ivan Postnikov

    Hello Sait Firat NEMIS

    The limitation is on infrastructure level and Plesk has no direct influence on it.

    So, the solutions are to ask ISP to unblock port if possible or to setup relay.

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  • Avatar
    Dennis Bronno Brouwer

    So I would need to Ask Google to open their Cloud Services on Port 25?

    For sure I already know the answer, I added a rule to the Firewall for port 2525 and I would like to use the SMTP server on that Port is that possible?

     

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    Phenneau

    this means no PLESK on Google GCP, a real constraint

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    Ivan Postnikov

    Hello,

    Dennis Bronno Brouwer Phenneau

    Google Cloud doesn't open port 25 for anyone.

    However, there's a workaround, see the details here.

     

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    Phenneau

    indeed, GCP will not open Port 25, and yes the workaround , it works, we went for SendGrid but there is huge constraint for webhosters: each domain must be validated by endgrid, that means 3 records per domain. Each new domain must be manually validated over the SendGrid platform. We havent figured out yet out to have our Server IP validated for all the domains.More over they are costs associated with the workaround.

     

    Regards

     

    Philippe

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