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I am experiencing an SMTP sending issue with Thunderbird on macOS.

Thunderbird Connectivity
Ark Chen
Ark Chen

Environment:

  • macOS, Apple Silicon (aarch64)
  • Thunderbird: 155.0.1 (aarch64), Release channel
  • Email hosting provider: Hostinger
  • SMTP server: smtp.hostinger.com
  • SMTP configuration: Port 465, SSL/TLS, Normal Password authentication

Problem: Incoming email via IMAP works normally, but Thunderbird cannot send any outgoing email.

The error is either:

“The connection to Outgoing server (SMTP) smtp.hostinger.com timed out.”

or:

“Sending of the message failed. The message could not be sent because connecting to Outgoing server (SMTP) smtp.hostinger.com failed. The server may be unavailable or is refusing SMTP connections.”

Troubleshooting already performed:

  • Webmail can send emails normally.
  • Thunderbird can receive emails normally.
  • SMTP settings and username have been verified.
  • Port 465 with SSL/TLS does not work in Thunderbird.
  • Port 587 with STARTTLS was also tested and does not work.
  • Tested with a different network/mobile hotspot — same issue.
  • Tested Thunderbird Troubleshoot Mode — same issue.
  • Updated Thunderbird from 155.0 to 155.0.1 — issue persists.
  • Direct TCP connectivity from the same Mac was tested successfully:

nc -vz smtp.hostinger.com 465 → succeeded

nc -vz smtp.hostinger.com 587 → succeeded

Therefore, the SMTP server is reachable from the Mac on both ports, and the same mailbox can send normally through Hostinger Webmail, but Thunderbird fails to establish/use the SMTP connection.

Since sending was working normally before the Thunderbird update and stopped afterwards without any SMTP configuration changes, this appears potentially related to the recent Thunderbird update.

Could you please advise whether there are any known SMTP/TLS/socket issues with Thunderbird 155.x on macOS, or any additional diagnostics/settings I should check?

Environment: * macOS, Apple Silicon (aarch64) * Thunderbird: 155.0.1 (aarch64), Release channel * Email hosting provider: Hostinger * SMTP server: smtp.hostinger.com * SMTP configuration: Port 465, SSL/TLS, Normal Password authentication Problem: Incoming email via IMAP works normally, but Thunderbird cannot send any outgoing email. The error is either: “The connection to Outgoing server (SMTP) smtp.hostinger.com timed out.” or: “Sending of the message failed. The message could not be sent because connecting to Outgoing server (SMTP) smtp.hostinger.com failed. The server may be unavailable or is refusing SMTP connections.” Troubleshooting already performed: * Webmail can send emails normally. * Thunderbird can receive emails normally. * SMTP settings and username have been verified. * Port 465 with SSL/TLS does not work in Thunderbird. * Port 587 with STARTTLS was also tested and does not work. * Tested with a different network/mobile hotspot — same issue. * Tested Thunderbird Troubleshoot Mode — same issue. * Updated Thunderbird from 155.0 to 155.0.1 — issue persists. * Direct TCP connectivity from the same Mac was tested successfully: nc -vz smtp.hostinger.com 465 → succeeded nc -vz smtp.hostinger.com 587 → succeeded Therefore, the SMTP server is reachable from the Mac on both ports, and the same mailbox can send normally through Hostinger Webmail, but Thunderbird fails to establish/use the SMTP connection. Since sending was working normally before the Thunderbird update and stopped afterwards without any SMTP configuration changes, this appears potentially related to the recent Thunderbird update. Could you please advise whether there are any known SMTP/TLS/socket issues with Thunderbird 155.x on macOS, or any additional diagnostics/settings I should check?

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