get the default email from the user on a Linux box

Question

Is there any way to programmatically get the current user's email address? I know the email is usually user@hostname but is there any I can get the email? I know how to get the username and the hostname so I can build it myself, but I want to be sure that I get the email address even when the email is not user@hostname.

Code in C is appreciated.

Thanks

Answer 1

Prompt the user for their email. If you have no guarantee that the email is user@hostname, then how else do you expect to determine what their email is other than asking them?

Answer 2

There is no standard mapping of user accounts to RFC822 (i.e. user@domain) email addresses. Generally, a default setup of typical mail transfer agents will accept local mail to addresses without a domain and deliver it to the user account of the same name. But even that can't be relied on, as you may not even have an MTA.

Answer 3

It depends how the user is stored. In a simple passwd file there's no email address, only a username. But you can have additional information with other authentication method like LDAP or SQL.

Answer 4

You can't get the actual email address in any standard way. I would try to send the mail to just username. Chanses that it will end up on the correct domain are actually not that bad ...

Answer 5

There is no such standard mapping of user account to email address - at least not for ordinary /etc/passwd derived accounts. Consider that a user might not even have an email address.

Answer 6

The UNIX way of doing this is to send email through the local mail-transfer-agent - simply invoking /usr/bin/mail is enough. The system administrator is responsible for configuring the local MTA to make sure email works properly.

• If you want to send email to the local user, just send it to their username - if they read their email somewhere other than locally, the MTA should be configured to forward it to them.

• If you just want to use the right "from" email address when sending email on behalf of a local user, so they get replies in the right place - again, just use their username. The MTA should be configured to do the right translation.

This way of doing things is good, because it means that this configuration only has to be done in one place (the MTA), rather than having to manually configure every single application on the box that sends or recieves email.