Resets failure count to 0.
MailBee.NET (in MailBee.NET.dll) Version: 12.3.0 build 647 for .NET 4.5
MailBee calls method each time the DNS server properly responds.
If, however, the DNS server was banned by MailBee due to multiple repeated failures,
the developer may call this method to force MailBee to use the DNS server again.