Source Mail
Read Identities
Enter all headers which should be read and used as a base to retrieve the identity. The order of the mentioned headers is important, addresses which were found earlier might be preferred for Selection at the End. Just give in as many names of headers as you like to look at. The default settings should work in most use-cases anyway. [1]
Sometimes headers are occurring multiple times in one email, by adding a ':' and a number you are able to select a special occurrence of a header. This means, 'received:2' will add all Identities found in the second received-header (beginning from top of the mail) to the list of possible Identities, 'received' will instead add all Identities from all received-headers to this list.
Another option is to add an ':@' to the selected header (for instance received:@'), this will only use the email address and ignore the rest, which is otherwise used as the Senders full name.
These options can be combined. For example, 'received:2:@' will only use the email addresses found in the second received header.
There will be no check, if the result is really any useful mail address - check this before adding additional headers by looking into your mail headers.
[1] activate the debug-output to understand what's going on
