can I use sendmail for SMTP instead of my ISP's SMTP server?
 

Hi. This may seem simple, but it has me baffled as to why my emails aren't getting through ...

The Problem: Either my ISP has a completely unreliable SMTP server, or there is something wrong with my network that prevents me from reaching it 9 times out of 10 (I still can send emails, but only after about 9 failures).

I thought I could solve the problem by using sendmail to act as my SMTP server (it says it's capable of it). I'm only trying to send emails originating from THIS computer (ie: 127.0.0.1). I have set up Thunderbird to send emails to an SMTP server at 127.0.0.1, and turned off authentication to try and simplify things. When I send a mail, Thunderbird says it's gone out successfully, but it never arrives at it's destination (it may be being spam-filtered, for all I know). I have my firewall set up to allow access to port 25, and I'm using the root account for these tests, so no user permissions should be getting in the way. I have checked the sendmail service, and it is running.

I haven't really modified any other files, like /etc/resolve.conf, or anything like that, since I didn't see that as relevant ... or am I mistaken?

So, is there anything I have forgotten? some silly mistake, or switch I was supposed to flick?

Any help would be appreciated.

The /etc/log/maillog, depending on your distro, should show you what's happening.

You don't need to modify your firewall for port 25, as that's only needed if you're receiving e-mails via smtp, not sending.

Your problem may be down to how other system "trust" your ISP. Some systems will only accept e-mails if the e-mail originates from the ISP's mail server, and not an IP within the ISP's "domain". This is to stop "hacked" machines being used to send spam.

Cheers.