If you want to send emails, don't run it from home. Most mail server will increase the spam level of an email coming from a dynamic ip or where the reverse dns doesn't match the name of the server.

If you just want to receive emails, then it depends how long is your downtime. Smtp requires that the sending server makes several attempts if the first failed, so if you are only off for a few minutes to a few hours, you will get your emails, just delayed. If full day downtime then this is not a viable solution.

If you need to send emails, then you kind of have to host your server in a datacentre. A cheap VM should probably be a good solution for a first attempt. You will still get downtime occasionally (update OS, update mail software, problem with your hosting provider). A cheap solution is to set up a failover server at home since it is only to receive emails while the primary server is down, with a lax retry policy (up to a few days).

A lot of IP ranges from cheap VM (and bare metal) providers are included in many blacklists since those ranges were (predictably?) abused by spammers in the past. Some companies are fighting this by denying outgoing traffic to port 25 until you fill a support ticket now, but whatever is in the blacklists will (probably) stay in the blacklists. Even buying your own IPv4 range does not guarantee it was not used by spammers in the past, and you will have to fight the blacklists owners to have it removed...

If you want to be sure your mail gets to someone else, things are going to be more complicated than setting up an SMTP+IMAP server combo, and after dealing with it in the past for work I'm happily outsourcing the pain to fastmail nowadays. :)

Blacklist owners are fairly reasonable. You do need to have an IP dedicated enough that your Reverse DNS can be set to your domain, and then pretty much all blacklists will honor a request to delist it or whitelist it. I've dealt with a couple of them at work.

You don't need to avoid it. Email was designed in the age of unreliable connections. It can withstand downtime just fine.

Almost every mail server retries for a few days, so you'll get your message, just late. Those few mail systems that don't retry have issues with greylisting - and unless you're fond of stories about Nigerian princes in distress, you're going to use that as the first anti-spam measure anyway.

It can only withstand so much downtime though. What if you don't have access to your server for a week? Heck, even a couple days can screw things up. So much email is time-sensitive. From transit delay notifications to message notifications and bank alerts... to actual humans that matter in your life trying to get something from you by tomorrow thinking you'll get their emails as usual. Maybe it's just me but I just don't see how "oh it's chill if my emails get randomly delayed for a day or two" would fly in today's world. Intentionally going off the grid after you've prepared for it is one thing, but having your email randomly go out without any warning in a potentially awfully inopportune time is quite something else...

> What if you don't have access to your server for a week?

Then you've chosen a bad service provider(s) to host/colocate/peer with.

Actually, you should notice this situation pretty much immediately you're online - because most likely your IMAP server would be down - and every single email client I've used had started to display warnings.

If you have more complex setup with separate MTA so your IMAPd may be online while your STMP service's unreachable, then you should set up monitoring system and deliver alerts either using local delivery or any out-of-band mechanisms (like SMS).

Also, you can set up a backup MX. Or two. Or more. Email has failover/HA since forever.