Outlook Express: Duplicate emails in sent items

Outlook Express: Duplicate emails in sent items

We have just moved to Zoho and when we send emails, Outlook Express is duplicating the sent items. Emails are going out only once as expected.

We have looked at this thread: https://help.zoho.com/portal/en/community/topic/outlook-duplicate-emails-in-sent-folder
Sadly this thread did not help much.

Is there a way to rectify this in Express?

Thanks in advance.