SMTP Mail Sending Problem Windows 7

[Adam Right]

Hi,

I am using SMTPClient class for sending mail from my C# application. I have
successfully sent mail in local area or outside of the domain.

But, i met a strange problem. When i send the mail to the client who uses
Windows 7 he cannot receive the mail, although exchange server tells me "it
has delivered".

I worked on it and i found a silly case. When i set MailPriority.High the
client receives the mail. If i do not set the mail priority to high, the
client does not receive the mail.

Can Anyone tell me what is the problem, or has anybody met a problem as
similar as with mine?

Thanks.