No Error Output if wrong mail credentials are used

If the incorrect details are used, for e.g. wrong password. Instead of returning an error, a PHP error is thrown, it might be better to return an error rather than PHP showing an error, that way a user response to that the credentials are wrong can be shown, rather than a PHP thrown error.

If I get time, I'll have a look at doing a PR for this.

While I think of it, I'm using this script in PHP7.1 on Linux Mint. I had to manually install imap, which most would have too. I'm thinking it might be good to check if imap is installed and return a message indicating that imap needs to be installed. New PHP'ers will just get a imap_open function isn't available, and won't know what to do. I'll have a look given time for this too.

[cnizzardini]

Thanks. If you want to do a pull and push to add this I'll merge it into the main codebase. I have not updated this code in quite sometime. I would like to begin updating some of my old projects and moving them into composer though. Your help would be more than welcomed if you are using this library extensively in a project of yours.

Thanks!