Without email, members won’t get email notifications of private conversations, thread updates, forum updates etc. It can also mean admin won’t get emails from members who are trying to get in touch with them using the contact form.
SMTP
How to Integrate Amazon’s SES For Sending Emails in XenForo?
XenForo not sending emails completely or emails aren’t delivered in members inbox? A step by step guide to verify your domain, create SMTP credentials and switch over to Amazon’s simple email services or SES in XenForo.