MacOS – Can not preview message in Mail.app

Simple answer - no, there is no easy way to tell from just the number.

However, I did a Google Image search for screenshots of the "About Mail" window, and found the following correlations between Mail version numbers.

• Mail 5.2 = 1257
• Mail 5.0 = 1244
• Mail 4.3 = 1081
• Mail 4.0 = 1075
• Mail 3.6 = 936
• Mail 3.5 = 930
• Mail 3.4 = 928
• Mail 2.1 = 752

If you're wanting to match to versions of the OS:

• Lion: 12xx
• Snow Leopard: 10xx
• Leopard: 9xx
• Tiger: 7xx

"About Mail" images found on these (and other) pages:

• http://www.ecu.edu/cs-itcs/mac/Apple-Mail-Settings.cfm
• http://gseis.ucla.edu/administrative-support-units/educational-technology-unit/etu-documentation/email-apple-mail

You could try deleting the "Envelope Index" files.

Run the following Terminal commands to backup and delete the files:

cd ~/Library/Mail/V2/
cp MailData MailData.old
cd MailData
rm Envelope\ Index Envelope\ Index-shm Envelope\ Index-wal

Alternatively…

1. Quit Mail

2. In Finder, press ⌘ cmd+⇧ shift+G

   Copy and paste the following

   ~/Library/Mail/V2/MailData/
   

   Press return or click Go

3. Backup then delete/move these files to the Trash:

   • Envelope Index
   • Envelope Index-shm
   • Envelope Index-wal

4. Relaunch Mail and wait for messages to import.

Note: once in a while this causes a corrupted message or two to reveal itself, usually in the form of having no "From" or "Subject" in the list view of messages (at least in "Classic Layout" mode).

Sometimes a corrupted message can actually screw up the interaction between Mail and the server, even if message is corrupted not on Mac, but on the server itself! (seen happen w/ AOL).