SMTP connection failure: SMTP failed to connect: received corrupt message of type InvalidContentType.
Delta Chat version
2.34.0 Android and 2.35.0 Windows 10
Expected behavior
Messages should be sent as before
Actual behavior
Outgoing messages stopped sending for one user for no apparent reason (showing only spinning circle animation) and the “Connectivity” settings say under “Outgoing Messages”: “Error: SMTP connection failure: SMTP failed to connect: received corrupt message of type InvalidContentType.”
The last message sent successfully was December 7, 9:24pm. Was that before a recent app update? Or did this user receive something that corrupted everything? Or did they send something that corrupted everything?
Restoring the account to a second DeltaChat device shows the same problem. Adding the account into a different SMTP email program shows no problem: normal emails can be sent and received without error on other email programs. No other users on the same server seem to have this problem. This is a Dovecot/Postfix server I set up before Chatmail existed.
The server’s TLS certificate was updated Dec 11 and is valid:
Issued On
Thursday, December 11, 2025 at 6:57:58 PM
Expires On
Wednesday, March 11, 2026 at 7:57:57 PM
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Should I make a totally new profile with the same account to see if that works? All of the previous encrypted messages will be unreadable in that case though, correct? deltachatlog.txt (32.3 KB)
Delta Chat has recently, since version 2.30, stopped sending SNI when using STARTTLS. It is normally not needed, but seems your server picks up wrong TLS certificate (for a different domain) in this case.
If you can, switch to implicit TLS (ports 465 for submission and 993 for IMAP). You can also go to advanced->relays settings and remove all advanced options (port, server hostname etc., leaving only the address and password, delta chat should find the correct port automatically then).
You’re right! This is the only user with ports configured manually for the servers and it is a virtual domain on the server with several domains. Removing all advanced options in the relay settings didn’t help though. It had errors about accessing “smtp.example.com” except the server hostname is “mail.example.com”. Setting the advanced options to “accept invalid certificates” makes it so that messages can be sent again though. Or changing the outgoing SMTP to the server that it is reading the TLS certificate for also works.
I thought I did have implicit TLS on port 465 enabled, but maybe I have to look into that more and learn how to do that correctly.
this is a Delta Chat SMTP/TLS issue, not data corruption. since newer versions stopped sending SNI on STARTTLS, your server is likely returning the wrong cert for that hostname, which triggers the InvalidContentType error.
that’s why it works when you:
accept invalid certificates, or
switch SMTP to the hostname that matches the cert
best fix: use implicit TLS on port 465 and make sure the SMTP hostname matches the certificate. restoring the profile won’t help this is purely a TLS negotiation issue.