If you want to send e-mail(s) to your Office 365 users using Virto action "Send e-mail with attachments" and Office 365 SMTP you have to provide the following parameters in the workflow action.
1) SMTP Server: smtp.office365.com
2) SMTP Port: 587
3) SMTP User Login and SMTP User Password are required and they must be from your valid and active Office 365 user. Two factor authentication must be disabled for this user account.
4) Encryption Type: TLS
5) TLS Version: 1.2
6) EmailFrom: must be the same as SMTP User Login.
If you use Office 365 SMTP server you can send e-mail(s) to Office 365 users only.