DnsServerTryTcp Property
Gets or sets if MailBee can make DNS queries via TCP.

Namespace: MailBee.DnsMX
Assembly: MailBee.NET (in MailBee.NET.dll) Version: 11.2.0 build 590 for .NET 4.5
Syntax
public bool TryTcp { get; set; }

Property Value

Type: Boolean
If true, MailBee will also make DNS TCP query in case if DNS UDP query returned no data or if there was no UDP query at all; if false, only DNS UDP queries are allowed. The default is true.
Exceptions
ExceptionCondition
MailBeeInvalidStateExceptionAn attempt to set this property to false when the current state of DnsServer object denotes that DNS UDP queries are disabled (UdpRetryCount is 0).
Remarks

UDP always precedes TCP. TCP can only be tried if UDP fails or if UDP was disabled at all.

For making DNS MX queries, leave this value true (some DNS servers like Google's 8.8.8.8 provide meaningful replies in TCP only). The same applies to DKIM/DomainKeys checks.

For making DNS RBL queries (actually, DNS A requests), it's better to disable TryTcp for performance sake. The nature of DNS RBL query is that if no requested A record is found, it simply means the respective IP address is not in the blacklist, it's not an error of any kind. Therefore retrying with TCP would be waste of resources.

If DNS UDP queries are disabled (UdpRetryCount is zero), this property must remain true (otherwise, neither TCP not UDP would be available for making a DNS query).

See Also