Hi. I'm wondering if could get some help. What I'm trying to do is setup an email server for a domain. I've got a combination of PostFix, Cyrus-IMAP and SpamAssassin running and it works really well. I'm just having one problem, though.

Right now, the goal is to be able to access the server in order to download and send email from anywhere (both inside and outside the firewall). However, I don't want to have an open relay for spammers to do whatever with. I've been reading up on SMTP-Auth, but I'm left with a few questions about it.

If I setup SMTP-Auth, obviously this will require my MUA's to authenticate themselves before they can send. However, will this prevent servers, which seem to also communicate on port 25, from sending email to my domain? For instance, right now, if I open port 25 on my firewall, I can receive email from GMail and other servers. But, if I place SMTP-Auth on that port, will those servers still be able to communicate with my server to send mail?

Any help would be greatly appreciated.

Thanks!

No it won't prevent you receiving mail, authentication is only required to send mail (ie relay) whereas if you have set postfix up correctly it will accept mail from anywhere for valid users on your system. Postfix is generally secure out of the box.

Perfect. Thank you very much.