Cannot connect to specific mail-provider (IMAP/SMTP/CalDAV) on specific local account

Question

I cannot connect to a specific mail provider using Apple's Mail (IMAP/SMTP), Calendar (CalDAV) and so on (Internet Accounts) on OS X 10.10.4. On trying to connect, I'm asked for my password which is not accepted. I have been in contact with the provider itself, my settings are sound. Additionally, I found the following:

• other mail-providers (e.g. gmail) work fine
• other machines on the same network work fine
• if I use another Application, i.e. Thunderbird, everything works as expected
• if I create another local account, Mail and Calendar also work there

This leads me to believe that this must be a problem located somewhere within the configuration of my current, local account. I tried to manually remove settings related to Mail and Calendar in ~/Library/ , but to no avail

Does anyone have a similar problem and knows where to look? How can I reset the apppropriate configurations, supposedly everything related to Internet Connections, Mail, Calendar and so on?