Increase SMTP session timeout to 1 minute

Summary:
10 seconds is not enough to connect, establish a TLS session (STARTTLS)
and perform the HELO handshake on high-latency networks, like airplane
WiFi. Sending emails works just fine for non-encrypted connections, but
fails with "connection lost" on encrypted ones, even though tcpdump
shows there is traffic going on. We managed to trace this to this
10-second timeout.

Reviewers: marten, knauss, dfaure, dvratil, mlaurent

Reviewed By: dfaure

Subscribers: KDE PIM

Tags: KDE PIM

Differential Revision: https://phabricator.kde.org/D12053