We recently enabled starttls to every destination (announcing the starttls extension).
We now see a lot of "454 4.3.3 TLS not available due to temporary reason" in reply to the STARTTLS by a big B2B italian provider named Aruba. We usually are able to send the email after 2-3-5 attempts, so this is not causing "failures" but mainly delay, but randomness could even cause permanent failures. Now, I read a forum where someone said Google try TLS delivery for 1 day, then they switch to plain text delivery if the delivery didn't happen in the first 24 hours. What do other senders do? Is this "try TLS for a while then switch to plain text" a best practice or just something "invented" by Google? Or do you use whitelist/blacklist in order to decide valid TLS destinations? I also have similar messages by other targets, but thet are very low volume, so I didn't investigate them: - 454 4.7.0 TLS not available due to local problem - 454 4.3.0 TLS not available due to local problem - 454 TLS currently unavailable - 454 TLS missing certificate: error:02001002:system library:fopen:No such file or directory (#4.3.0) ) Stefano PS: this is my first post and www mailop org is not working right now so I've not been able to check the "posting guidelines" to see if this kind of message is allowed or not in this list.
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