Helpdesk Mails are sent with the addition "on behalf of..."

Helpdesk Mails are sent with the addition "on behalf of..."

Hey there,

I have a problem to set "from" address for e-mails sent form zoho desk - it always showing "on behalf" information like:  support=mydomain@eu-service.mailer.zohosupport.com; on behalf; Helpdesk IT <helpdesk@mydomain>

What I did:

-set "from" adres using my own SMTP server and verified e-mail address (heldpesk@mydomain)
-enabled the address
-assigned the address to appropriate department
-changed "from address" on templates and enabled them 

Unfortunately all communication (including automatic reply) is with "on behalf" information -  etc. Only answers from the ticket agent are sent with the correct from address without the addition "on behalf".

Thank you in advance for your support.

Christopher