Hi @djenk,
depending on your WordPress mail configuration additional error messages can be stored with the mail. If there were error messages you can hover over this icon or find the details in the detail view of a mail.
Not all mail plugins provide this error details because of poor integration. But the plugins listed here do: https://ww.wp.xz.cn/plugins/wp-mail-logging/#installation
This is a list (subset) of errors that can occur:
SMTP Error: Could not authenticate.
SMTP Error: Could not connect to SMTP host.
SMTP Error: data not accepted.
Message body empty
Unknown encoding:
Could not execute:
Could not access file:
File Error: Could not open file:
The following From address failed:
Could not instantiate mail function.
Invalid address:
mailer is not supported.
You must provide at least one recipient email address.
SMTP Error: The following recipients failed:
Signing Error:
SMTP connect() failed.
SMTP server error:
Cannot set or reset variable:
Extension missing:
