Email can not be sent

Email can not be sent

Hi, I'm testing my email with test@scopicsoftware.com, it has a strange issue.

1/ When I tried to sent email with the subject  [DSSP]: Welcome! and the subject like this.

Dear test ,
You have been invited to join the Developer Self Support.
Follow this link to activate your account:
http://dev-dssp.scopicsoftware.com/account/activate/c5bdbb208a084f158c637349c3cc95ef

Sometimes it sent, sometimes I can't received the email.

2/ When I changed to content to simple content like "Test", the email is sent okay every time.

So how can I send this email?
I assume that Zoho will filter spam automatically, right?

Regard,
Tung.