I'm a .Net developer. I make an mail activation system for our customers;

When they register our site we send and email (from noreply@yazililargaranti.com) to activate their membership by a link.

And I get an error about this service:

Mailbox unavailable. The server response was: 5.4.6 Mail rate exceeded limit. <a href=https://mail.zoho.com/UnblockMe target=_blank>Click here</a> to unblock.

I know that there is a limit, this is understandable. 

However, this mail activation system is not a campaign. 

Please show me a way to do that and unblock our noreply mail.

Thank you so much!