Emails to Coworkers on old email server are not sending or receiving

Emails to Coworkers on old email server are not sending or receiving

I have my new Zoho account working for the most part but when I send an email from my account to a coworker that is using the Siteground email server, it does not arrive.  Also, when they send me an email from the siteground server it does not arrive.  I do not have very much confidence in this product because I have no clue if my emails are being sent or received and vice versa.  I have setup the DKIM and SPF for authentication and all of the MX details are correct.  I have also the set the priorities correctly.