You might argue that this is a Vodafone issue because they supplied the device, but the truth is more likely to be that no one at the network has the expertise to solve the issue, and particularly not if it's service-related. It's odd that this has happened since a reset rather than a system update (or was the reset following one?) In that case, there could be a new version of the email app that, for some reason, isn't communicating with your business acount SMTP server.
There are, however, a number of things you can try.
1. POP instead of IMAP
2. Security settings for SMTP
3. Clearing the app cache and data in the main Settings menu. Actually, I'd probably start with that as something may be hanging over from the previous setup.
I assume that you're using Gmail through the email (rather than the dedicated) app? That, of course, probably sets up automaiically, being a popular service. The fact that you can do that (assuming you are), suggests there's nothing wrong with the app itself.
Also, have you tried doing the setup over both wifi and mobile data? If the email service is linked to an ISP, they sometimes don't like SMTP connections that aren't over their own network, or (occasionally) mobile ones. Again, though, the fact that it worked previously is odd.
If none of the suggestions above works, you may need to speak to the service provider, and maybe also Samsung as the app is theirs.
