Is there a size limit on the file that can be sent using mailx?

I'm trying

mailx -s "alertlog" tome@work < /dir/my.log

and I only get a portion of the log. The newest portion of the log is not included in the mail.

Additionally, I would like the option of mailing just the last 100 lines of the file. How would I add the tail -100 syntax to the mail command.

If it matters, I'm running this from the crontab.

Thanks for any input.

Donna