fix: set get_max_smtp_rcpt_to for chatmail to the actual limit of 1000 instead of unlimited. (#7432)

adb brought this up in an internal discussion.
With the recent introduction of channels it becomes easier to hit the
limit
and it becomes impossible to send messages to a channel with more than
1000 members, this pr fixes that.

---------

Co-authored-by: Hocuri <hocuri@gmx.de>

src/context.rs

@@ -545,7 +545,7 @@ impl Context {
             .and_then(|provider| provider.opt.max_smtp_rcpt_to)
             .map_or_else(
                 || match is_chatmail {
-                    true => usize::MAX,
+                    true => constants::DEFAULT_CHATMAIL_MAX_SMTP_RCPT_TO,
                     false => constants::DEFAULT_MAX_SMTP_RCPT_TO,
                 },
                 usize::from,