For inbound, I use Postfix + rspamd + dovecot directly to my server. Outbound, I used to send it directly from my server. I did this 15+ years with DKIM, DMARC, and SPF. It worked well for like 95% of the emails I sent, but I started relaying through smtp2go.com after I had just a couple really important emails not get delivered or me not be sure if the recipient saw them.