How can you get Outlook & other mobile devices mail clients to warn you if you are about to send an email to an external domain?

• Moved by Jason Johnston [MSFT]Microsoft employee Friday, September 11, 2015 1:32 PM Not a development question.

Hi S-3200,

Thank you for your question.

I agree with  Nithyanandhams suggestion. By my testing, mobile devices mail client could not support MailTips. In addition, there are the following we should be concerned:

1. MailTips aren't supported when working in offline mode in Outlook.
2. When a message is addressed to a distribution group, the MailTips for individual recipients that are members of that distribution group aren't evaluated. However, if any of the members is an external recipient, the External Recipients MailTip is displayed, which shows the sender the number of external recipients in the distribution group.
3. If the message is addressed to more than 200 recipients, individual mailbox MailTips aren't evaluated due to performance reasons.
4. Custom MailTips are limited to 175 characters.
5. If the sender starts composing a message and leaves it open for an extended period of time, the Automatic Replies and Mailbox Full MailTips are evaluated every two hours.

If there are any questions regarding this issue, please be free to let me know.

Best Regard,

Jim