If the mail sent from skyconnect user to an outside domain user couldn't reach the recipient and the user is not getting any failure or bounce email. In such cases first, check the outbound mail flow whether the mail was sent properly from skyconnect server or not.
If the mail is showing sent/queued to the recipient server, then check the incoming logs on SpamTitan for the sender if there's any bounced mail that got blocked or quarantined for that user.
https://docs.mithi.com/home/quarantine-management-console-for-end-users-on-spamtitan
https://docs.titanhq.com/en/1139-view-mail-history.html
In many cases, the bounce email having the envelop sender field as empty can cause the blocking of that mail in spam filtering.