Switches from rusqlite to sqlx to have a fully async based interface
to sqlite.
Co-authored-by: B. Petersen <r10s@b44t.com>
Co-authored-by: Hocuri <hocuri@gmx.de>
Co-authored-by: link2xt <link2xt@testrun.org>
Previously MX records were queried only for OAuth 2 configuration and
did not affect the list of servers tried. User was required to manually
configure the servers for Google Workspace (former GSuite) domains.
Now MX records are queried during configuration. If provider is found in
offline database, its ID, corresponding to the filename, is saved as
`configured_provider`.
`configured_provider` is also set during database migration if email
address uses the domain from the provider database, but no MX querying
is done.
providers may have a maximum for the SMTP RCPT TO: header,
therefore, an outgoing message is split into several chunks.
the chunk size defaults to 50, however, if known to be larger or smaller
by a dedicated provider, this setting may be changed.
this does not affect the MIME To: headers,
if a provider has a maximum here, this is change would not help.
It was used when timeout was set on the whole smtp.send() operation.
Now only the operations inside smtp.send() can timeout, and such timeout
errors result in SendError, so SendTimeout is unused.
