Emailing and Link Trouble

Hi,

I am having trouble with Invoices, Orders and now Quotes Not emailing from MYOB. I check the sent emails section and they have not gone. 

Can it be a Form Format issue, not linking when updates get sent to us?

Also when Invoices are sending I am being informed the client receiving is not able to open the Invoice Link to acquire there invoice, and I am being asked to send a PDF by email.

Any ideas or Help would be muchly appreciated as usual.

Thank you again.

Kermie