Bash scripting in a Maildir directory

I want to grep across 500 files in a Maildir directory. I issued the command grep MyPattern * I got the error message: bash: /usr/bin/grep: Argument list too long So I stored the list of files in a file MyFiles, and issued the following for i in $(cat MyFiles); do echo $i; done Before I did a grep, I wanted to do an echo just as a check. But this gave the following error bash: 1434361691.M617282P6399V0000000000000808I00000000000E16C1_23.ananda-linux,S=10055:2,S: command not found where that 1434... thing is the first file in the directory. So back to the original question. How do I grep across all these files in the mailbox. And I have larger mailboxes containing 50000 or more emails.