You have a legacy application that needs to send email to employees.
The legacy application must send email by using SMTP through Exchange Online.
You need to identify the correct host name and port information.
Which settings should you use?
A.
Smtp.office365.com and port 587
B.
Outlook.office365.com and port 25
C.
Outlook.office365.com and port 587
D.
Smtp.office365.com and port 25
A.
https://support.office.com/en-us/article/POP-and-IMAP-settings-for-Outlook-Office-365-for-business-7fc677eb-2491-4cbc-8153-8e7113525f6c?ui=en-US&rs=en-US&ad=US
https://blogs.msdn.microsoft.com/carloshm/2016/05/10/how-to-send-a-new-message-using-smtp-in-office365/
https://support.office.com/en-us/article/How-to-set-up-a-multifunction-device-or-application-to-send-email-using-Office-365-69f58e99-c550-4274-ad18-c805d654b4c4
Option A and Option D both are correct.I would go with Option A (port 587 recommended)