To change the SMTP port in Business Process Automation (BPA), complete the following steps:
Right-click on the Send Email (SMTP) tool found under Advance BPA, System, Tools, Output, and select Properties
The SMTP port setting is on the Advanced tab of the SMTP Settings dialog (you may or may not have the Authentication and Connection Security checkboxes ticked)
Please note that many ISPs are now blocking SMTP traffic on port 25. According to office365 docs, port 25 can get throttled, so they recommend using port 587.
If you are unable to send emails but are able to receive them, you may need to change your outgoing SMTP server port to 26 or 587. Once you have changed the default Port in SMTP, you will have to change the port No in BPA and click on the Test Connection button on the Main tab to test the connection.