I just setup a test account on your hosting account and was able to login to the account without any problems.
Please be sure to verify that ALL the things listed in the “I cannot login to webmail” are not the case on your account. Also be aware of copy-pasting additional spaces and other blank characters.
MX records affect where and how new incoming email is received. Nothing more. It doesn’t affect your ability to access webmail and view email which has already been received.