When I try to send an email tells me that the username and password is incorrect and is not. In the server logs shows me the following.

Code:
Aug 18 17:49:57 zimbra saslauthd[21225]: zmauth: authenticating against elected url 'https://zimbra.xyz.com:7071/service/admin/soap/' ...
Aug 18 17:49:57 zimbra saslauthd[21225]: authentication against url 'https://zimbra.xyz:7071/service/admin/soap/' caused error 'curl_easy_perform: error(56ceived HTTP code 403 from proxy after CONNECT'
Aug 18 17:49:57 zimbra saslauthd[21225]: url 'https://zimbra.xyz.com:7071/service/admin/soap/' will not be used for (at least) 600 seconds
Aug 18 17:49:57 zimbra saslauthd[21225]: Authentication cycle re-elected url https://zimbra.xyz.com:7071/service/admin/soap/, giving up ...
regards