sending failed reason 554-5-1-8 sender address blocked

sending failed reason 554-5-1-8 sender address blocked

I just opened a zoho account yesterday and transferred my contacts from gmail. I have sent e-mail address update to all of them and was blocked afterward. I am pretty sure I do not have over 250 contacts... Please help and advise how to prevent this in the future, since I did not send 250msg in 1 day.
My account: andrejch@zoho.com
Thank you
Andrej