Is there an easy way to know that an email contains an attachment without opening the message? John Carter tells us, "Yes. There is a column that can be made visible in Mail that will show a small paperclip image if a message contains an attachment, and in addition, it will be accompanied by a number identifying how many attachments are in that message. If you don’t see that paperclip for a message that has an attachment, then you can set up Mail to show it.
Right click on any column header in Mail to open a menu. You should see something like the following menu (using Mail version 4.4):

Notice that the top item is “Attachments.” If it isn’t checked, click on it.
After activating that column, it will appear on the far right of the column list (above all the message headers).

You can drag that column to any position in the header I like it closer to the far left:

Here's an example of what you could see:

The blue dot shows me which email I haven’t read.

There you are. Enjoy knowing which message has an attachment and how many it contains."

Note: John sends me an attachment and the icon says "tiff." But I can't use it; I need a "jpeg." I drag the attachment by its icon over to the desktop. Clicking on it there opens it in Preview. I go to the menu at the top, choose File, then Save As. From the drop-down Format list I choose "jpeg" and I choose to save it to the desktop. Now I can copy the "jpeg" to the blog.