If your server is not “online” you could vpn into your home network and use it that way. Another option is to have it local, meaning for example with bit/vault-warden you can still view your passwords if you don’t have connection. But you can’t edit or add new ones
I wrote a blog some time ago why selfhosting email sucks
https://nx2.site/email-selfhosting
If you just want the email server for only you and your friends, or for internal messages, selfhosting email can be fun, but your main email should probably not be selfhosted.