Hi sharamateti,
the problem you are have described is caused by the format of the e-mail message sent from ServiceNow. Usually e-mail can be plain message, or multipart message that can contain text/plain or text/html part. It can contain both at the same time. Service Desk is not smart enough to read text/html part. So in case your e-mail contains only text/html part, it will create ticket without description and summary and message will be in attachment as you experienced.
Make sure that other party is sending e-mail in format that Service Desk accepts.
In the source of the e-mail should be message text following the subject line, or if it is multipart message, then there should be Content-Type: text/plain; charset="UTF-8" part and not only Content-Type: text/html; charset="UTF-8" part.
For debugging purposes it is always useful to set server rule on exchange server, that stores copies of incoming messages in a folder. This way it is preserved for later investigation. Same can be done in gmail where you assign label upon message arrival. These messages can be then copied to inbox while you are debugging it.
To see more information about maileater processing you can increase level of maileater logging by running command:
pdm_logstat -n pdm_maileater_nxd 201
and when not needed, disable it by running
pdm_logstat -n pdm_maileater_nxd
It will give you more information on why e-mail was not processed. Sometimes it is that message doesn't match rule, sometimes it is missing mandatory field. The stdlog will tell you. It is also helpful to be able to read Service Desk responses, because they contain reason why ticket was not created. But by increasing log level you will get content of that message too.
Marek Vitek