Nothing quite matches the gut punch of being on time for a deadline then having to push it back to troubleshoot mail problems. Or losing a weekend because while you know enough to get started your experience isn't deep enough to fix deliverability problems in a timely manner.
> I work on an opensource SMTP server. I build both opensource and proprietary solutions related to mail. I will likely open a commercial mail service next year.
Translation:
"I am an intelligent guy who works hard. My entire professional career is devoted to designing and maintaining mail systems. I work full time to achieve mastery of my craft. Yet I can't understand why people outside my specialization might find it difficult to do my job."
Email _is_ hard. That's why I'm very happy to outsource mail to experts like OP.