Gmail is giving me error message when sending from GMAIL using "SEND MAIL AS"

Gmail is giving me error message when sending from GMAIL using "SEND MAIL AS"

Hi, 

No one from Zoho has returned to me with assistance with this matter so I am hoping someone out there can help out. 

When I created my email through zoho, I went to GMAIL and set up POP3/IMAP and "send mail as" in settings. 

So now I was able to send emails from google using my Zoho email address as well as receive emails from my ZOHO email into GMAIL. 

I sent an email to a list of contacts to let them know I have a new email. I did not know that this is considered a "mass email" and that it's prohibited. So i received error messages from gmail that these emails did not go through. 

Now, I am unable to send ANY email using my Zoho email through GMAIL

I am receiving the following error message: 
Diagnostic-Code: smtp; 550 5.4.6 Unusual sending activity detected.



What can I do to be able to send emails from this account again using GMAIL???

Please help! 

AA