Recently wrote a small program is to write your own code shall not apply to other software will file sent out in the form of attachment, the final result is that if the file you can use a text document right open then send right, but if a word or picture will be garbled words, here is my code Mime format, don't know what's the problem you see,
StrCmd=szdate;//date
StrCmd +="From:" + szFrom + "\ r \ n";
SzTo strCmd +=", "+ +" \ r \ n ";
StrCmd +="Subject:" + szsubject + "\ r \ n";
StrCmd +="Mime - Version: 1.0 \ r \ n";
StrCmd +="content-type: multipart/mixed; The \ r \ n ";
//note above these strings before does not have space to the top to the
StrCmd +="is a boundary=" __=_Part_Boundary_001_011991. 029871 \ \ r \ n \ r \ n ";//this must keep one or more Spaces in front of the

StrCmd +="-- __=_Part_Boundary_001_011991. 029871 \ r \ n";
StrCmd +="Content - Description: enclosed photo \ r \ n";
StrCmd +="content-type: text/plain. The \ r \ n ";
//in front of the roof to the
StrCmd +="charset=" gb2312 \ \ r \ n ";//in front of the empty one can at least know need a space between the parameters and the front type of
StrCmd +="Content - Transfer - Encoding: base64 \ r \ n \ r \ n";

StrCmd +=Base64Encode (mailContent c_str ()) + "\ r \ n \ r \ n";//email content

StrCmd +="-- __=_Part_Boundary_001_011991. 029871 \ r \ n";
StrCmd +="content-type: PNG image/PNG; The \ r \ n ";
//the above to
Printf (" filename==========");
Const char * pszName=: : STRRCHR (" c: "(pszFilename, '\ \');
if (! PszName)
PszName=pszFilename;
The else
PszName++;
Filename=pszName;
CoutStrCmd +="name=" + filename + "\ r \ n";//in the same way at least one empty
StrCmd +="Content - Transfer - Encoding: base64 \ r \ n \ r \ n";
Send (sockfd, strCmd c_str (), strCmd. The length (), 0).
//strCmd. Delete (0, strCmd. Length ());



//strCmd +=fileDate + "\ r \ n \ r \ n";//file binary encoding data into base64

/* multiple attachments transmitted
StrCmd +="-- __=_Part_Boundary_001_011991. 029871 \ r \ n";
StrCmd +="content-type: application/octet - stream; The \ r \ n ";
StrCmd +="name=" + filename + "\ r \ n";//in the same way at least one empty
StrCmd +="Content - Transfer - Encoding: base64 \ r \ n \ r \ n";


StrCmd +=fileDate + "\ r \ n \ r \ n";//file binary encoding data into base64
*/
//send the body
Printf (" is read the file... \n");
If (ReadFromFile (pszFilename, filename, sockfd)==false)
{
Printf (" file read failure \ n ");
return ;
}

String strCmd1;
StrCmd1 +="\ r \ n \ r \ n - (=_Part_Boundary_001_011991. 029871 - \ r \ n";
StrCmd1 +="\ r \ n \ r \ n";
//end. Note here to multiple blank lines
//the above string together good sent to the server can
Send (sockfd, strCmd1 c_str (), strCmd1. The length (), 0).
Memset (buff, 0, sizeof (buff));
Recv (sockfd, buff, sizeof (buff), 0).
Printf (" send success! \ n ");
return ;
}