Re: Check for blacklists
Also, some ISP could block port 25, in an attempt to block some spammer, or spam botnets. I had little issues as long as I was self-employed and could buy a "business" ADSL and fixed IP (just, it required a VAT number), when I moved to another job as an employee, and had to switch to a "consumer" ADSL, my server could no longer work and I had to move it to a rented VM - I still can manage my own server, but of course data are stored on someone's else - you can encrypt and whatever, still less control. On the bright side, it has a far faster connectivity to the Internet, my ADSL is limited at 1Mb upload (another issue with "consumer" ones), and sending large mails is not fast at all.
Other factors to take into account it's you need your own domain name, and a DNS configured with the proper MX record(s). If you're going to use DKIM or the like, you need also to be able to set them up in the DNS records. Some mail server could perform reverse DNS lookups, and reject connections that doesn't match.
To use SSL/TLS properly, you need certificates - buy them, or you can easily generate them yourself. I would suggest to avoid simple self-signed ones (MITM could be too easy) - generate your own CA(s), trust it on your devices, and then generate certificates from that.
To block spam I would suggest to use DSNBL services (i.e. Spamhaus, etc.) at the connection level, because they can reject an incoming connection before the actual mail is sent, reducing the server load (Spamassassin may be a bit heavy if it has to process everything).
As soon as a server is accessible from outside behind your router/firewall, you have also to ensure it doesn't become an entry door inside your LAN, not it can be used for spam. You need to know how to properly harden everything.