Is it practical to run a private SMTP server on a static IP in 2020/2021?
I have a small piece of static IP4 space (5 IPs, /29) and general Linux sysadmin capabilities. I have run SMTP servers before, but I don't know what the current state-of-the-art for email and spam-filtering is.
I can set up the necessary authentication features to prevent spammers from abusing my server, but I'm concerned that mail from my site will be spamholed, RBL'd or refused for some authentication thing that I either don't know about or can't reasonably implement. (I guess one example would be if a neighboring /29 block was spamming, and the RBLs just kicked everything in the /24 out. That would be miserable.)
I would prefer to run my own server, because my experience with non-Google service providers is mixed (I'm not a big enough customer to get or afford RIGHT NOW tech support when they have problems) and I don't want Google reading my mail any more than they do already.
Is SMTP something that a "small company"-level entity can reasonably run themselves in 2020/2021? Or is the attack surface too large (so it requires a lot of administration)? Or do other mail exchangers downgrade/refuse mail from non-backbone sources in order to cut down on their spam?
If you are technically competent and if your IP block is not mapped to a DSL/home user range, yes its practical. You will want SPF records and reverse DNS at a minimum. You will also not want very large bursty volumes. Save for spam filtering incoming mail its fairly low effort to maintain - although doing decent spam filtering can be time consuming.
Another thought - your incoming and outgoing SMTP servers can be different, and I think most mailnservers arnt to concerned about reputation of who they send mail to (while being very concerned a out who they receive mail from)
If your ISP offers it, you can often set your outbound mail server to relay all outbound mail through them, which further reduces your delivery reputation concerns.
Good answer from @davidgo and a shortcut might be to first look up your IPs - do a 'spam blocklist check' - google mentions first:
- https://mxtoolbox.com/blacklists.aspx
- https://www.dnsbl.info
If they're a mess to start, you'll see and maybe give up.
Beyond SPF, I you'll also need to know about rDNS, DMARC and DKIM if you're not relaying through your ISP's mail server for outgoing.