That’s the problem. I changed the authentication code (for other reasons) in the mailer daemon, and I gave OAUTH2 a higher priority than PLAIN, when no setting exists (and the UI don’t give the possibility to change the authentication mechanism). Yahoo is exposing in its capabilities that XOAUTH2 is supported, so the mailer daemon choose it, but there is no support for it on Sailifsh side…
We can check this with @ahjolinna, can you check what the following command is giving :
devel-su -p ag-tool get-service 13 email string:imap4/authentication
To work, it should return imap4/authentication = 2 (2 means PLAIN) but it will report imap4/authentication = 4 (4 means XOAUTH2) in your case, right ? (ag-tool comes in the package libaccounts-glib-tools)
You can then change it for 2 using :
devel-su -p ag-tool update-service 13 email string:imap4/authentication="2"
If it works, then, we can think about CalDAV and CardDAV issues…