**Update**
The below instructions are for older builds of Nintex Workflow. The ability to update the port number has been added to the "Messaging and Notifications" settings of Nintex Administration in later builds.
Question
When I change my outgoing email settings in Central Administration > System Settings > Configure outgoing e-mail settings to use Port 587 for O365 SSL email my email is received as expected from SharePoint Workflows but my Nintex workflow send notification emails fail and the ULS logs are showing that they are still being sent to port 25.
Answer
To resolve this issue the web.config needs to be altered to point Nintex Workflow send notification emails to the correct port by adding the below.
<system.net> <mailSettings> <smtp from="test@foo.com"> <network host="smtpserver1" port="587" userName="username" password="secret" defaultCredentials="true" /> </smtp> </mailSettings> </system.net>
Additional Information
The reason this issue occurs is because Nintex uses the API System.Net.Mail.SmtpClient.Send to send emails which is different to Sharepoint which uses SPUtility.SendEmail and this is why the results differ from SharePoint to Nintex.
Related Links
Information sourced from this blog post : Sending Email with System.Net.Mail