Approval Request errors

meriame

i,
I have à problemes in approvals request and i need your Help.

1.when i try to send an Approval Request for first time from a purchase order,i receive mails succefully .but when try the second time from an other purchase order i got an error(see picture).
i cant resolve the problem and i cant understand it.

2.i I noticed that the database (dynamics navision)become soo Heavy when i send just one approvals request from purchase order.
can you give me a reasons for those two problémes??.
thinks for help

this is a message error tha appear in the picture:

The SMTP mail system returned the following error:(0x80040213):
transportation to fail in its connection to the server

thinks