Required capabilities
A client is a potential fit when it supports authenticated SMTP submission over STARTTLS and lets you set the sender to the connected mailbox.
- Server: the hostname displayed by smtpify365
- Port: 587
- Connection security: STARTTLS
- Authentication: required, using the generated SMTP username and one-time password
- Envelope sender: the Microsoft 365 mailbox that authorized the connection
Current protocol boundaries
The service accepts SMTP PLAIN and LOGIN only after TLS is established. It does not offer implicit TLS on port 465, unauthenticated relay, inbound email, POP, or IMAP.
Current service limits
The SMTP process currently enforces the following technical limits. Microsoft 365 can apply additional mailbox and tenant limits.
- 25 MB maximum message size by default
- Up to 100 recipients in one SMTP envelope
- 30 new connections per minute from one remote address
- The envelope sender must exactly match the connected mailbox, ignoring letter case
Test before relying on it
Create a connection, send a small plain-text message to an address you control, and then test the real workflow and attachments. A built-in test button may not exercise the same path as an order, backup, scan, or alert.