Hi Sea-wing
Did you find out what the problem was as I am having the same problem with one of my clients. My logs show the email is sent successfully, I also received a copy. But my client did not receive this email with attachment. Then we tested an email without the attachment and this one worked. After this, I have tested an email to her using outlook with an attachment and she received this OK. so this is the issue I cannot understand
1- customer receives emails from outlook using the same email as my system email with or without pdf attachment; so my email is not spammed by her outlook
2- she can receive emails from WHMCS without any pdf attachements
3- she cannot receive any emails from WHMCS with pdf attachements
4- other clients can receive emails from WHMCS with attachements.
What do we need to check on her email settings so she can receive invoice or direct emails from WHMCS with pdf attachments. This is very unusual, may be you have found a solution for the similar problem you experienced.
I look forward to hearing from you, thanks in advance
Aladdin