This seems to be caused by Adguard HTTPS filtering. Disabling Adguard should allow Mailbird SMTP STARTTLS connections to complete without issue and the emails to send properly.
Articles in this section
- I cannot send/receive emails anymore
- I can't receive or send email anymore
- Microsoft 365 SMTP authentication unsuccessful error while sending emails
- Yahoo/AOL/AT&T/Verizon account is not downloading/syncing messages
- Cannot send emails / Error sending email / Emails go to drafts
- Emails fail to send / Sending error/ Emails stay in drafts
- When I reply an email, it disappears from the Inbox
- "Server authentication failed" message (Yahoo, Hotmail, etc)
- Error sending mail from AOL
- Error sending mail: 'A call to SSPI failed, see inner exception'