Are you sure that you don’t use any Encryption or Authentification? It would be helpful to see what your server-side SMTP Log is telling. Your message tells me, that your Exchange Server identify your Sender or Computer as something from outside your Domain.
Ah I guess the “myemail” part solved that. No relaying generally means this SMTP server doesn’t want to send an email on behalf of another domain. Does “myemail” = “myemail@myexchange.com”?
If this is an internally hosted Exchange server, it’s possible that this hostname resolves to the “public” or internet facing connection, which very likely is configured to not allow SMTP client connections for sending mail (relaying). Internal clients usually connect to a different hostname that only resolves on the internal network.
I have the same problem: what do you mean please with "We had to allow a specific IP to send relays "? Is it something to ask to the exchange manager? Is it something in the cose? I go on with SSLconnected=false…