Could just be a problem with the account in eM Client causing it and might just need removing and re-adding to fix it.
If you have an eg: IMAP, Exchange, or iCloud (non pop) account, I would then suggest to backup eM Client via “Menu / Backup” and remove and re-add your account and see if that fixes the sending mail problem.
To remove and re-add your account once backed up, go to “Menu / Accounts” and then click on your acct on the left and then click delete / remove along the top. Lastly re-add your account via either the automatic email wizard or manual option depending on your mail server.
If still a problem sending mail, click “Menu / Operations” in eM Client and look for any error messages that appear in the errors and log tabs.
dear cyberzork, thank you
I noticed that it works if I change in SMTP , Security criteria from Forza l’utilizzo di SSL/TLS
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