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I just setup postfix but I just realized my ISP outgoing blocks port 25 (SMTP). How do I send email outside? I can see my mail queue is filling up. Any suggestion?

  • How about talking to your ISP whether they have lost their mind? – Hauke Laging Nov 26 '14 at 16:52
  • It shouldn't block you from sending out emails. Your mailserver does not use port 25 as its source when sending emails out. – Sree Nov 26 '14 at 16:56
  • sorry i just update my question it was outgoing – Satish Nov 26 '14 at 17:04
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    Are you on a Corporate ISP Plan? WikiPedia says "Some Internet service providers intercept port 25, redirecting traffic to their own SMTP server regardless of the destination address. This means that it is not possible for their users to access an SMTP server outside the ISP's network using port 25. Some SMTP servers support authenticated access on an additional port other than 587 or 25 to allow users to connect to them even if port 25 is blocked, but 587 is the standardized and widely-supported port for users to submit new mail." – eyoung100 Nov 26 '14 at 17:31
  • We are have purchased VM server from big hosting company, just like cloud hosting company. 587 port does require SMTP auth? – Satish Nov 26 '14 at 18:00
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If your ISP is blocking outbound port 25, you've probably made a bad choice in the location of your mailserver. Because port 25 is blocked, I am assuming you have a machine inside your home/office, vs using a server.

I would highly recommend that you take what you've learned from setting up postfix and install it on a cheap VPS. It is not a good idea to have an intermittent mailserver, or one that jumps IPs.

Otherwise, your option is to get a cheap VPS and create a tunnel, but in doing this you'll most likely have to add the tunnel's ip to a TXT spf record, which starts complicating things.

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    I agreed, later when i talk to ISP folks they said, they will provide you smarthost where you can relay emails for outdoing.. it is their policy to reduce IP blocking by blacklister – Satish Nov 27 '14 at 15:21
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If you don't have a static IP address, you shouldn't be sending email directly to the Internet. Kudo's to your ISP for blocking the spambots on their network from reaching me. Even if you were allowed to send email, many hosts would refuse your mail or route it to the spam box. Configure you mail server to send via your ISP's relay server. Many configurations have an option for using a smart host for delivery via a relay.

If you get a static IP address, it is likely your ISP will allow you to send to port 25. However, if you want your mail delivered there are several things you should do. You may want to review my Email Policy or my rant on Running an Email Server.

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