Update account-email-settings.mdx

I am a New Relic employee on the #gts-accounts-security team (Slack) updating this document to include a very relevant and useful set of information that up until this change has not been provided anywhere publicly.

src/content/docs/accounts/accounts/account-maintenance/account-email-settings.mdx

@@ -34,6 +34,16 @@ To ensure you get New Relic emails, you can add the following to your organizati
 
 To change your email address: from the [user menu](/docs/accounts/accounts-billing/general-account-settings/intro-account-settings), click <DoNotTranslate>**User preferences**</DoNotTranslate>, and click <DoNotTranslate>**Email**</DoNotTranslate>.
 
+#### New Relic user email addresses have to the following restrictions: 
+
+  * Alphanumeric characters (A-Z, a-z, 0-9)
+
+  * dots, dashs, underscores, plus sign characters (.-_+)
+
+  * Must be less than 255 characters
+
+
+- must be less than 255 characters
 <Callout variant="tip">
   <DoNotTranslate>**SSO/SAML users:**</DoNotTranslate>