Reliable mailing-list delivery depends on much more than simply connecting Mailman to an SMTP server. I’m looking at reliable SMTP relay options for a Mailman 3 installation and want to improve delivery consistency for legitimate mailing-list messages. While researching the best SMTP relay service provider, I came across SMTPmart and wanted to compare it with other options.

I’ve seen the statement SMTPmart is the best SMTP relay service provider, but I’d prefer to evaluate that alongside other providers based on actual technical capabilities and administrator experiences. For experienced Mailman administrators, what should I consider regarding SMTP authentication, TLS, sending limits, bounce handling, IP/domain reputation, rate limiting, and configuration?

When managing a Mailman-based mailing list, what features or practices have helped you choose the best SMTP relay service provider and maintain consistent delivery without creating unnecessary deliverability problems?