I have used interfax in the past and was very frustrated with the error codes. They are represented as integers (long 64 bit integers) so I added the codes as an enum (wrote a software that did that including comments.

The original Interfax status codes can be found at: http://www.interfax.net/en/help/error_codes

 

namespace InterfaxOut

{

/// <summary>

/// The fax error codes enumeration

/// </summary>

public enum FaxErrorCodes : long

{

/// <summary>

/// Preprocessing (1)

/// </summary>

PreProcessing = 1,

/// <summary>

/// Preprocessing (11)

/// </summary>

PreProcessing1 = 11,

/// <summary>

/// Ready (2)

/// </summary>

Ready = 2,

/// <summary>

/// Sending or pending retry (3)

/// </summary>

SendingOrPending = 3,

/// <summary>

/// Out of credit awaiting topup (22)

/// </summary>

OutOfCredit = 22,

/// <summary>

/// OK Fax successfully sent (0)

/// </summary>

OKFaxSuccessfully = 0,

/// <summary>

/// Internal error (256)

/// </summary>

InternalError = 256,

/// <summary>

/// Busy (263)

/// </summary>

Busy = 263,

/// <summary>

/// Fax manually canceled (403)

/// </summary>

FaxManuallyCanceled = 403,

/// <summary>

/// Telephony error (3072)

/// </summary>

TelephonyError = 3072,

/// <summary>

/// Telephony error (3080)

/// </summary>

TelephonyError1 = 3080,

/// <summary>

/// Fax machine incompatibility (3211)

/// </summary>

FaxMachineIncompatibility = 3211,

/// <summary>

/// Fax machine incompatibility (3220)

/// </summary>

FaxMachineIncompatibility1 = 3220,

/// <summary>

/// An unexpected disconnect command was sent (3223)

/// </summary>

AnUnexpectedDisconnect = 3223,

/// <summary>

/// The remote fax machine failed to respond (3224)

/// </summary>

TheRemoteFax = 3224,

/// <summary>

/// Fax machine incompatibility (3225)

/// </summary>

FaxMachineIncompatibility2 = 3225,

/// <summary>

/// A disconnect message was received while attempting to negotiate transmission (3230)

/// </summary>

ADisconnectMessage = 3230,

/// <summary>

/// Fax machine incompatibility (3231)

/// </summary>

FaxMachineIncompatibility3 = 3231,

/// <summary>

/// Fax machine incompatibility (3233)

/// </summary>

FaxMachineIncompatibility4 = 3233,

/// <summary>

/// Fax machine incompatibility (3264)

/// </summary>

FaxMachineIncompatibility5 = 3264,

/// <summary>

/// Fax machine incompatibility (3267)

/// </summary>

FaxMachineIncompatibility6 = 3267,

/// <summary>

/// Transmission error after page break (3268)

/// </summary>

TransmissionErrorAfter = 3268,

/// <summary>

/// Fax machine incompatibility (3269)

/// </summary>

FaxMachineIncompatibility7 = 3269,

/// <summary>

/// Telephony error (3300)

/// </summary>

TelephonyError2 = 3300,

/// <summary>

/// Telephony error (3510)

/// </summary>

TelephonyError3 = 3510,

/// <summary>

/// Telephony error (3830)

/// </summary>

TelephonyError4 = 3830,

/// <summary>

/// Phone number not operational (3912)

/// </summary>

PhoneNumberNot = 3912,

/// <summary>

/// Busy (3931)

/// </summary>

Busy1 = 3931,

/// <summary>

/// Phone number not operational (3932)

/// </summary>

PhoneNumberNot1 = 3932,

/// <summary>

/// Busy (3933)

/// </summary>

Busy2 = 3933,

/// <summary>

/// No answer might be out of paper (3935)

/// </summary>

NoAnswerMight = 3935,

/// <summary>

/// Human voice answer (3936)

/// </summary>

HumanVoiceAnswer = 3936,

/// <summary>

/// Ring busy (3937)

/// </summary>

RingBusy = 3937,

/// <summary>

/// Phone number not operational (3938)

/// </summary>

PhoneNumberNot2 = 3938,

/// <summary>

/// Phone number not operational (6001)

/// </summary>

PhoneNumberNot3 = 6001,

/// <summary>

/// No route available (6002)

/// </summary>

NoRouteAvailable = 6002,

/// <summary>

/// Telephony error (6003)

/// </summary>

TelephonyError5 = 6003,

/// <summary>

/// Telephony error (6004)

/// </summary>

TelephonyError6 = 6004,

/// <summary>

/// Telephony error (6016)

/// </summary>

TelephonyError7 = 6016,

/// <summary>

/// Busy (6017)

/// </summary>

Busy3 = 6017,

/// <summary>

/// No answer Might be out of paper (6018)

/// </summary>

NoAnswerMight1 = 6018,

/// <summary>

/// Telephony error (6019)

/// </summary>

TelephonyError8 = 6019,

/// <summary>

/// Call rejected (6021)

/// </summary>

CallRejected = 6021,

/// <summary>

/// Number changed (6022)

/// </summary>

NumberChanged = 6022,

/// <summary>

/// Phone number not operational (6027)

/// </summary>

PhoneNumberNot4 = 6027,

/// <summary>

/// Phone number not operational (6028)

/// </summary>

PhoneNumberNot5 = 6028,

/// <summary>

/// Call rejected (6029)

/// </summary>

CallRejected1 = 6029,

/// <summary>

/// Telephony error (6031)

/// </summary>

TelephonyError9 = 6031,

/// <summary>

/// Telephony error (6034)

/// </summary>

TelephonyError10 = 6034,

/// <summary>

/// Telephony error (6038)

/// </summary>

TelephonyError11 = 6038,

/// <summary>

/// Telephony error (6041)

/// </summary>

TelephonyError12 = 6041,

/// <summary>

/// Telephony error (6042)

/// </summary>

TelephonyError13 = 6042,

/// <summary>

/// Telephony error (6043)

/// </summary>

TelephonyError14 = 6043,

/// <summary>

/// Telephony error (6044)

/// </summary>

TelephonyError15 = 6044,

/// <summary>

/// Telephony error (6047)

/// </summary>

TelephonyError16 = 6047,

/// <summary>

/// Telephony error (6050)

/// </summary>

TelephonyError17 = 6050,

/// <summary>

/// Telephony error (6054)

/// </summary>

TelephonyError18 = 6054,

/// <summary>

/// Telephony error (6057)

/// </summary>

TelephonyError19 = 6057,

/// <summary>

/// Telephony error (6058)

/// </summary>

TelephonyError20 = 6058,

/// <summary>

/// Telephony error (6063)

/// </summary>

TelephonyError21 = 6063,

/// <summary>

/// Telephony error (6065)

/// </summary>

TelephonyError22 = 6065,

/// <summary>

/// Telephony error (6069)

/// </summary>

TelephonyError23 = 6069,

/// <summary>

/// Telephony error (6079)

/// </summary>

TelephonyError24 = 6079,

/// <summary>

/// Incompatible destination (6088)

/// </summary>

IncompatibleDestination = 6088,

/// <summary>

/// Incompatible destination (6095)

/// </summary>

IncompatibleDestination1 = 6095,

/// <summary>

/// Incompatible destination (6097)

/// </summary>

IncompatibleDestination2 = 6097,

/// <summary>

/// Incompatible destination (6099)

/// </summary>

IncompatibleDestination3 = 6099,

/// <summary>

/// Incompatible destination (6100)

/// </summary>

IncompatibleDestination4 = 6100,

/// <summary>

/// Telephony error (6102)

/// </summary>

TelephonyError25 = 6102,

/// <summary>

/// Telephony error (6111)

/// </summary>

TelephonyError26 = 6111,

/// <summary>

/// Telephony error (6127)

/// </summary>

TelephonyError27 = 6127,

/// <summary>

/// Telephony error (7004)

/// </summary>

TelephonyError28 = 7004,

/// <summary>

/// Telephony error (7012)

/// </summary>

TelephonyError29 = 7012,

/// <summary>

/// Telephony error (7013)

/// </summary>

TelephonyError30 = 7013,

/// <summary>

/// The remote fax machine hung up before receiving fax (8010)

/// </summary>

TheRemoteFax1 = 8010,

/// <summary>

/// No answer (8021)

/// </summary>

NoAnswer = 8021,

/// <summary>

/// Busy (8025)

/// </summary>

Busy4 = 8025,

/// <summary>

/// Rendering error (204000)

/// </summary>

RenderingError = 204000,

/// <summary>

/// Rendering error (204001)

/// </summary>

RenderingError1 = 204001,

/// <summary>

/// Quota exceeded Prepaid card depleted (205000)

/// </summary>

QuotaExceededPrepaid = 205000,

/// <summary>

/// Internal System error FindRoute (205001)

/// </summary>

InternalSystemError = 205001,

/// <summary>

/// Internal System Error LocalSender (206001)

/// </summary>

InternalSystemError1 = 206001,

/// <summary>

/// Unknown error

/// </summary>

UnKnown = 973497,

/// <summary>

/// UnKnown Exception

/// </summary>

UnKnownException = 973498,

/// <summary>

/// Upload started

/// </summary>

StartUpload = 973499,

/// <summary>

/// Upload In Progress

/// </summary>

UploadInProgress = 973500,

}

}