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I have modified my postfix submission port from 25 to 587. Yet it doesn't block mails being submitted from mynetworks or php scripts residing on server for submitting emails to be sent through port 25.
My question is if I change the port in PHP from 25 to 587, will it force authorisation? As on port 587 I have enabled authorisation submission.
Thanks.
Joshi
Posted 2017-09-07T19:02:15.010
Reputation: 133
From what I can tell, you've only moved one program's use of port 25 to 587, which also requires TLS-encryption off the top of my head. You'll need to move all other programs use of port 25 to port 587 also, unless you want to setup an iptables rule to forward all traffic from 25 to 587, which I don't recommend - that would still leave programs configured to use port 25, which isn't what you're wanting.
Keep in mind the TLS part of port 587. I think most mail servers will deny your mail without a certificate being sent with it, which you could obtain from LetsEncrypt for free. – Dooley_labs – 2017-09-07T19:07:18.547
my aim is block malicious use of contact forms, scripts in php file from sending mail without using any password. my question is if I change the port in php from 25 to 587. Normally mail won't be send without using smtp. I think it will work like that or am I not in the right path. – Joshi – 2017-09-07T19:17:47.963
Perhaps use of Google's ReCaptcha would suit your situation better. It's free to use and easy to implement. I use them on all of my php-based contact/sign-up sites. This tutorial may be of-use.
– Dooley_labs – 2017-09-07T19:20:08.993I am not designing/developing all the websites on my server. some spaces are given to client. who may or may not implement captcha. – Joshi – 2017-09-07T19:42:38.203
In that case, an iptables rule would probably work. From this question you may be able to use
– Dooley_labs – 2017-09-07T19:51:55.340iptables -A PREROUTING -t nat -i -p tcp --dport 25 -j REDIRECT --to-port 587to achieve your goal. If it works, don't forget toiptables-save. If it doesn't work, switch the-Awith-Dto delete the rule. I'm assuming you may already know this based on your rep from other SE communities, but leaving it in for future reference.