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.