Emails not arriving at destination

[#1]

Thank you @Townman. My preference would be Duckduckgo, but I don't think they've released a Linux version yet. I'll try a few of the others.

Great Help, thanks.

[#2]

Thank you for introducing me to the word "nugatory".

[#3]

If you looked the word up, I hope you were offered the Latin root as meaning “of no force or effect” - in the context of testing from an environment which is not deemed a bulk sender, it is not a useful comparison of success of failure compared to a source which is deemed a bulk sender.

I note that American dictionaries' definitions are rudely dismissive, which is the wrong sentiment of the word.

[#4]

According to the OED it is a one-in-ten-million use (or thereabouts). Not a commonly used word (or a very rarely used word).

However, it appears that there is an assumption that this 'feature' only affects bulk senders (or senders 'deemed' to be bulk senders). I would be happier if there were data that supported (or didn't support) that assumption. Hence my 'interest'.

Dic had a duc with fer on it's bac and thats a fac (irregularly declined Latin verbs IIRC).

[#5]

'Bulk senders' is the premise of both Microsoft's and Gmail's actions.  They are very specific in the references these failure conditions point to.  That does not preclude they getting the implementation wrong elsewhere too.