[dijit]

I have a feature (called greylisting) whereby my server intentionally rejects the first mail it receives from a domain.

I have never had anyone claim that their mail has not been delivered to me, and I get a lot of mail.

Retry is built in to the spec, and if you’re really worried you can put a second “receive” SMTP server on the internet with a lower priority, and have it backhaul with LMTP.

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Email was designed in a time where hosts were not perpetually connected to each other.

[Symbiote]

GMail itself will sometimes temporarily reject messages, then accept them later.

I have Postfix logs showing things like "this address is receiving a high rate of email" which are later accepted.

[auxbuss]

Gmail always rejects the first email I send to a new gmail account. It does this every time – and has done for years – despite the fact I have sent emails to hundreds of other gmail accounts, and send emails to such accounts every day.

This is the reason I personally will not touch any Google services. And in business, I excise Google services as a priority. If a company cannot handle email in a civil manner, it certainly can't be trusted with anything of importance.