Mail app dropping setting

[rexone]

Okay, weirdest problem.
Mail has been working fine on my iMac Pro. Yesterday I suddenly start getting alert that says...
"SMTH AUTH is required for message submission on port 587"
...everytime I try to send mail.
I go into settings, check everything is set as it should be including outgoing server.
It verifies password etc. no problem then about 5-seconds afterwards it flicks back to 'No outgoing server selected' and all of the details entered have gone.
If I try to send mail in that 5-second window it will send but as soon as it reverts... nope. Broken.
Anyone have the slightest idea what is going on here?

 

[jpn]

Okay, weirdest problem.
Mail has been working fine on my iMac Pro. Yesterday I suddenly start getting alert that says...
"SMTH AUTH is required for message submission on port 587"
...everytime I try to send mail.
I go into settings, check everything is set as it should be including outgoing server.
It verifies password etc. no problem then about 5-seconds afterwards it flicks back to 'No outgoing server selected' and all of the details entered have gone.
If I try to send mail in that 5-second window it will send but as soon as it reverts... nope. Broken.
Anyone have the slightest idea what is going on here?

do you have other apple devices that also should be using common settings for this account, and, do you have Keychain sync enabled in iCloud preferences?

after ensuring the above, i have fixed similar issues by then going to Mail/Preferences/Accounts/(email account) Server Settings/then ensuring that Automatically manage connections settings is turned off.
then going into Outgoing Mail Server, clicking account and then retyping in the correct server, and making sure that incorrect (old, no longer used, etc) are faithfully deleted.

it may take any time from a couple of minutes to several days for iCloud servers to catch up to yr changes that you need synced across devices.
ensure you have yr correct settings in yr other devices as well.
but i can remember one time a while ago when i needed to delete the account on my other devices and reset it up on all devices to get it working.

port 587: correct password type is MDS Challenge-Response. this setting often times appears as blank or turns into an incorrect setting and multiple attempts to get it to stick on its correct setting are sometimes needed.

 

[rexone]

Do you have Keychain sync enabled in iCloud preferences

Bingo!
This is super weird... I'm sure it had not been switched on but somehow it was selected. I'm the only one that admins the account so not sure what's going on.
If it had been on it's been so for quite some time so why did it randomly decided to delete the entry & default to that...
Anyhews... you're a legend. I've deselected Keychain and now it's working as expected.
Thanks!