The line limit is likely BUFSIZ which can be 4096
Note the following about setting up mail aliases in /etc/aliases:
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Mail aliases in /etc/aliases are public. This means that if you set up a mail alias called softball, anyone can send to softball@your-machinename and make use of the mail alias.
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When the mail is sent, /etc/aliases mail aliases are not expanded. For example, if you send mail to softball@machinename, that's how the mail reads when it is received. The recipients know what the mail alias is, but not necessarily who else is on it.
The format of mail aliases that are created in /etc/aliases is somewhat different from those in .mailrc. Each /etc/aliases alias should use the following format:
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The name of the mail alias, followed by a colon (
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The recipients (logins and machine names), separated by commas. Note that the mail alias does not have to be on a single line.
To modify your /etc/aliases file, you must first become root. If root is password protected, you'll need to know the root password.