Due to the case that I think, that you have missing micro patches, I would recommend using the command:
/usr/local/psa/admin/bin/autoinstaller --select-product-id plesk --select-release-current --reinstall-patch --install-component base
... in the first place. ErrorCode 1 is pointing to an external mail service - usage in one of your domain subscriptions and this issue/problem should be corrected with one of the micro updates. With my first post, I just wanted to make sure, that you check the resolutions as well, because you could have checked your FTP - backup server with this KB - article, to make sure, that the issue/problem isn't caused by a false username and password and no firewall blocking.
If you still experience the same issue/problem, please try the current bootstrapper, which corrects quite a lot of problems:
/usr/local/psa/bootstrapper/pp12.0.18-bootstrapper/bootstrapper.sh repair
If you still experience issues/problems, please reply with the newest error logs and error descriptions, because they might be different, after the suggestions above. Please include then as well your operating system, the current Plesk version and the latest MU installed.