Problem after moving to new server

Hello,
I have recently moved my shop to a new server. Now I have this problem (I'm using OC Version 2.3.0.2):
Customers that are NOT logged in can't send email using the "Contact Us" page or they can't reset their password using the "Forgotten Password" page.

This is the error message I receive by email when a customer try to use the "Contact Us" page (a similar error message is received if they try to reset the password).
Is not working only if they are NOT logged in - if they are logged in It works perfectly.
----------------------------
Error message :

This is an automatically generated Delivery Status Notification.

Delivery to the following recipients was aborted after 0 second(s):


Action: failed
Status: 5.1.1
Diagnostic-Code: smtp; 550 5.1.0 lW5y2000S1lfaGW01W6XEG invalid domain
Last-attempt-Date: Mon, 05 Aug 2019 20:06:31 +0200
-----------------------

Thanks in advance for any help.

Worked before?
When you moved to the new server..the password for the email is the same?
You have checked if SMTP settings are correct?

Hello,
yes, it was working before.

I'm using the "Mail" protocol not the SMTP in my system settings

Solved:
I found an old post when somebody suggested to change from:
-fyouremail.xxxx.com
to
-Fyouremail.xxxx.com

And It worked!