Q3. Can you suggest a better way of doing this check? (Basically I want to at least check the syntax of the address and that the domain exists, and I want a result within a second.)

Maybe you're already doing that, but in case not: Definitely cache the result. I recommend this because it's very likely that a) the senders are regularly mailing to the roughly same recipients b) the validity of a recipient is probably quite static. It doesn't really make sense to check if an email address is valid multiple times a day.

You could then use this list of 'probably valid' email addresses and try to actually talk to the receiving mail server and see if it would accept an email with this recipient (no need to actually send the mail - you can abort the exchange as as soon as the mail server accepts the recipient). If the address is rejected then you can update the status from 'probably valid' to 'invalid'.

In reply to Re: Mail::CheckUser inconsistent results by Monk::Thomas
in thread Mail::CheckUser inconsistent results by tel2

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