(Objective-C) Email Received Header Fields

Received emails will contain one or more "Received" header fields at the beginning of the email header. Each SMTP server (along the delivery path) adds a Received header to the top of the incoming message. The delivery route can be ascertained by the sequence of Received headers. There is a good summary of the Received header here.

The following explanation is taken from the reference URL above:

In theory, the value of a Received field is tokenizable. It contains

    1) optionally, a "from" atom followed by an encoded domain name;
    2) optionally, a "by" atom followed by an encoded domain name;
    3) optionally, a "via" atom followed by another atom;
    4) zero or more of the following: a "with" atom followed by another atom;
    5) optionally, an "id" atom followed by either (1) an atom or (2) a < token, an encoded address, and a > token;
    6) optionally, a "for" atom followed by an encoded address;
    7) a semicolon; and
    8) a timestamp. 

In practice, SMTP servers put all sorts of badly formatted information into Received lines. It is probably best for readers to treat everything before the final semicolon as unstructured text, purely for human consumption.

This example demonstrates iterating over each of the Recevied headers and getting the content of each.

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#import <CkoEmail.h>
#import <CkoStringBuilder.h>

CkoEmail *email = [[CkoEmail alloc] init];

// Load a .eml file into the email object.
BOOL success = [email LoadEml: @"/home/users/chilkat/eml/myEml.eml"];
if (success == NO) {
    NSLog(@"%@",email.LastErrorText);
    return;
}

CkoStringBuilder *sbHdrName = [[CkoStringBuilder alloc] init];

int i = 0;
int numHeaders = [email.NumHeaderFields intValue];
while (i < numHeaders) {
    [sbHdrName SetString: [email GetHeaderFieldName: [NSNumber numberWithInt: i]]];
    if ([sbHdrName ContentsEqual: @"Received" caseSensitive: NO] == YES) {
        NSLog(@"%@%@",@"Received: ",[email GetHeaderFieldValue: [NSNumber numberWithInt: i]]);
    }

    i = i + 1;
}