I have a problem, my ISP reconfigure their servers so port 25 always closed, and while calling them they mentioned that they working on the problem but without a deadline for solving. While using telnet on port 25 OR 587 it says "421 service not available (configuration error, try again later)" All of us and our clients can't send mails, the in bounded mails arrives (mails on the same server), but out bounded mails failed (mails outside our servers) our servers has installed ISPConfig 3, postfix ... so what should i do to overcoming these problem !!
the problem not in my server , port 25 locked in ISP's server not my one .. so if i changed the port to any other it also won't work
Change your relay settings accordingly in Server Config > Mail e.g. [smtp-relay.gmail.com]:587. You can also use the same for system mail in System Config > Mail.
I know this is a late answer but for the sake of others with same problem, the answer is definately a mail service relay host using port 2525. Checkout Sendgrid...its a simple process to get working and is free for low usage.
i have been using https://www.authsmtp.com/ for the past 8 years and it is very easy and cheap to use. i think i pay 35 bucks a year for 2 gigs of mail a month. they give great support and have a great write up for what you need to do. and they use port 2525
Well guys, The problem is ISP blocked the port, most of the ISPs do that, due to spamming concern so simply use alternative port like 26 or use startls on port 587, configure your email server accordingly and you are good to go..
That's true for clouded server which dont allow ports for emails.. You can simply go with alternate solution..
