To send and receive email notifications, GLPI requires a mailbox with IMAP / POP3 and SMTP access enabled.
It appears people like to use their Gmail as the email service provider, which can be a little tricky to set up. Here is how a correct Connection String of a GLPI receiver for Gmail looks like:
Feel free to set other variables as you prefer, like maximum size of received email or which date to use as a ticket date. If you are going to allow importing of big emails, we recommend making sure you can support it long term. Every attachment will be stored on your GLPI server after picking it up from mailserver.
Screenshot of a typical Gmail GPLI mail above.
For Followup configuration (outbound email) just enter a hostname, port, and others as when setting up Gmail in any other email client.