Change Outbound Sendmail Port

tomlaino · 03-27-2014, 01:37 PM

I am sure this is a basic question and I am sure it has been asked and answered many times over on this forum but I cant seem to find the answer that I am looking for.

I am using CentOS 6 with sendmail. My ISP blocks port 25 for outbound mail. I need to use port 587 but I cant seem to find where to change it. I have tried looking through sendmail.cf but I dont see anything definitive that should be changed. Any help would be appreciated.

Ser Olmy · 03-27-2014, 05:00 PM

I assume you use an M4 macro file to generate sendmail.cf?

According to this blog post, this is how you specify an alternate port number for a Smart Host:

Code:

define(`SMART_HOST’,`isp.smart.host’)dnl
define(`RELAY_MAILER_ARGS’,`TCP $h 587′)dnl

I haven't actually tried this myself, so YMMV.

tomlaino · 03-27-2014, 09:13 PM

Ok. So I have a question. I am not using an ISP. My sendmail server is on a LAN (server.mycompany.local). So what would I put where isp.smart.host would be?

This works on my other servers where port 25 is not blocked.

Ser Olmy · 03-28-2014, 12:46 AM

When you said you needed to "use port 587", I assumed you meant "I need my local mail server to use port 587 on my ISP's Smart Host for all outbound mail".

Using port 587 for outbound mail in general without using a Smart Host isn't going to work, for the simple reason that the majority of mail servers on the Internet doesn't listen on port 587. If you cannot send mail directly to other servers on TCP port 25, you will have to relay all outbound mail via the Smart Host provided by your ISP.