Zoho Sign Not Delivering

Zoho Sign Not Delivering

I have sent several contracts out via Zoho Sign.   They do not seem to be getting delivered.  I had one person receive it, but the others have not.  

I had one person tell me they sent it back to me and never got it and doesn't show as signed.  I've sent to other people and they say they never get it. 

Is this a common issue?  Is there a fix?

Thanks.