i've got this error:
This message requires SMTPUTF8 extension and this SMTP server doesn't support it. This error is usually raised, when non-ASCII characters are used in a local part of an email address. Consider using SmtpMail.ForceASCIIMode method, only-ASCII local part email addresses or SMTPUTF8 compatible mail server.
And these are the extensions supported:
DSN, SIZE, STARTTLS, AUTH, ETRN, TURN, ATRN, NO-SOLICITING, 8BITMIME, HELP,
So there is no SMTPUTF8 ...