emails not being sent and/or delivered and no notification of this failure except from the customer asking where his email was

emails not being sent and/or delivered and no notification of this failure except from the customer asking where his email was

I sent an email on 1/22 that contained one sentence and two attachments - one attachment was 178kb and the other was approximately 450kb.

Today I received an email from an irate client demanding to know where my email was.

I checked my sent box and it indicates it was "sent." So, I forwarded the same email to my hotmail account.  That, too, has not been delivered.

further, emails addresses that I have REPEATEDLY marked as "not spam" still keep getting sent to spam...

Sadly, I am starting to migrate my account and contact information away from zoho... I just can't risk the loss of clients due to repeated failures...