[tsimionescu]

The email in my company all comes from @<company-name>.com. Why would a company keep a separate domain for internal vs external email? Is that common practice?

[michaelt]

It's rare but not unknown - for example Facebook employees' e-mails are [e-mail] rather than [e-mail] and sometimes facebook send e-mails from [e-mail] ¯\_(ツ)_/¯

[terinjokes]

Facebook's case is likely because they launched a public email service back in 2010.

[the_jeremy]

It's not internal vs external, it's employee vs users (e.g., @google.com vs @gmail.com)