MAPI in Delphi - working but crashing after mail is send - delphi

Question

I have been playing around with some code to send mail using MAPI in my Delphi XE7 program.
I have managed to get the To, Cc and Bcc working together with fileattachment, but when the mail is send by the client (in this case Outlook 2010) the program crashes and I simply can't figure out where I am am doing something wrong - I might be staring blind on the code.
I have made a small example with the code in a file in my dropbox
dl.dropboxusercontent.com/u/65392149/Mapi_MCVE.ZIP
The MAPI function looks like this
function SendMailMAPI(const aFrom, aTo, aCc, aBcc, aSubject, aBody: string; aMailFiles: TStringList; aReceipt: boolean): boolean;
var
MapiStatus: DWord;
MapiMessage: TMapiMessage;
MapiOrigin: TMapiRecipDesc;
MapiRecipient: array of TMapiRecipDesc;
MapiFiles: PMapiFileDesc;
RecipientsTo: TStringlist;
RecipientsCc: TStringlist;
RecipientsBcc: TStringlist;
RecipientsCount: integer;
FilesCount: Integer;
i: integer;
Filename: string;
begin
MapiStatus := SUCCESS_SUCCESS;
Result := True;
MapiFiles := nil;
FillChar(MapiMessage, Sizeof(TMapiMessage), 0);
if aReceipt then
MapiMessage.flFlags := MAPI_RECEIPT_REQUESTED;
MapiMessage.lpszSubject := PAnsiChar(AnsiString(aSubject));
MapiMessage.lpszNoteText := PAnsiChar(AnsiString(aBody));
FillChar(MapiOrigin, Sizeof(TMapiRecipDesc), 0);
MapiOrigin.lpszName := PAnsiChar(AnsiString(aFrom));
MapiOrigin.lpszAddress := PAnsiChar(AnsiString(aFrom));
MapiMessage.lpOriginator := nil;
FilesCount := aMailFiles.Count;
if FilesCount > 0 then
begin
GetMem(MapiFiles, SizeOf(TMapiFileDesc) * FilesCount);
for i := 0 to FilesCount - 1 do
begin
FileName := aMailfiles[i];
MapiFiles[i].ulReserved := 0;
MapiFiles[i].flFlags := 0;
MapiFiles[i].nPosition := ULONG($FFFFFFFF);
MapiFiles[i].lpszPathName := PAnsiChar(AnsiString(FileName));
MapiFiles[i].lpszFileName := PAnsiChar(AnsiString(ExtractFileName(FileName)));
MapiFiles[i].lpFileType := nil;
end;
MapiMessage.nFileCount := FilesCount;
MapiMessage.lpFiles := #MapiFiles^;
end;
RecipientsCount := 0;
RecipientsTo := TStringlist.Create;
RecipientsCc := TStringlist.Create;
RecipientsBcc := TStringlist.Create;
RecipientsTo.Delimiter := ';';
RecipientsCc.Delimiter := ';';
RecipientsBcc.Delimiter := ';';
try
if aTo <> '' then
begin
RecipientsTo.DelimitedText := aTo;
RecipientsCount := RecipientsCount + RecipientsTo.Count;
end;
if aCc <> '' then
begin
RecipientsCc.DelimitedText := aCc;
RecipientsCount := RecipientsCount + RecipientsCc.Count;
end;
if aBcc <> '' then
begin
RecipientsBcc.DelimitedText := aBcc;
RecipientsCount := RecipientsCount + RecipientsBcc.Count;
end;
FillChar(MapiRecipient, Sizeof(TMapiRecipDesc) * RecipientsCount, 0);
SetLength(MapiRecipient, RecipientsCount);
RecipientsCount := 0;
if RecipientsTo.Count > 0 then
begin
MapiRecipient[RecipientsCount].ulRecipClass := MAPI_TO;
for i := 0 to RecipientsTo.Count - 1 do
begin
MapiRecipient[RecipientsCount].lpszName := PAnsiChar(AnsiString(RecipientsTo[i]));
MapiRecipient[RecipientsCount].lpszAddress := PAnsiChar(AnsiString(RecipientsTo[i]));
Inc(RecipientsCount);
end;
end;
if RecipientsCc.Count > 0 then
begin
MapiRecipient[RecipientsCount].ulRecipClass := MAPI_CC;
for i := 0 to RecipientsCc.Count - 1 do
begin
MapiRecipient[RecipientsCount].lpszName := PAnsiChar(AnsiString(RecipientsCc[i]));
MapiRecipient[RecipientsCount].lpszAddress := PAnsiChar(AnsiString(RecipientsCc[i]));
Inc(RecipientsCount);
end;
end;
if RecipientsBcc.Count > 0 then
begin
MapiRecipient[RecipientsCount].ulRecipClass := MAPI_BCC;
for i := 0 to RecipientsBcc.Count - 1 do
begin
MapiRecipient[RecipientsCount].lpszName := PAnsiChar(AnsiString(RecipientsBcc[i]));
MapiRecipient[RecipientsCount].lpszAddress := PAnsiChar(AnsiString(RecipientsBcc[i]));
Inc(RecipientsCount);
end;
end;
MapiMessage.nRecipCount := RecipientsCount;
MapiMessage.lpRecips:= Pointer(MapiRecipient);
finally
RecipientsTo.Free;
RecipientsCc.Free;
RecipientsBcc.Free;
end;
try
MapiStatus := MapiSendMail(0, Application.MainForm.Handle, MapiMessage, MAPI_LOGON_UI + MAPI_DIALOG, 0);
except
on E:Exception do
ShowMessage('U_Mailing.Mapi.SendMailMAPI: ' + E.Message);
end;
for i := 0 to FilesCount - 1 do
begin
System.AnsiStrings.StrDispose(MapiFiles[i].lpszPathName);
System.AnsiStrings.StrDispose(MapiFiles[i].lpszFileName);
end;
for i := 0 to RecipientsCount - 1 do
begin
System.AnsiStrings.StrDispose(MapiRecipient[i].lpszName);
System.AnsiStrings.StrDispose(MapiRecipient[i].lpszAddress);
end;
case MapiStatus of
MAPI_E_AMBIGUOUS_RECIPIENT:
Showmessage('A recipient matched more than one of the recipient descriptor structures and MAPI_DIALOG was not set. No message was sent.');
MAPI_E_ATTACHMENT_NOT_FOUND:
Showmessage('The specified attachment was not found; no message was sent.');
MAPI_E_ATTACHMENT_OPEN_FAILURE:
Showmessage('The specified attachment could not be opened; no message was sent.');
MAPI_E_BAD_RECIPTYPE:
Showmessage('The type of a recipient was not MAPI_TO, MAPI_CC, or MAPI_BCC. No message was sent.');
MAPI_E_FAILURE:
Showmessage('One or more unspecified errors occurred; no message was sent.');
MAPI_E_INSUFFICIENT_MEMORY:
Showmessage('There was insufficient memory to proceed. No message was sent.');
MAPI_E_LOGIN_FAILURE:
Showmessage('There was no default logon, and the user failed to log on successfully when the logon dialog box was displayed. No message was sent.');
MAPI_E_TEXT_TOO_LARGE:
Showmessage('The text in the message was too large to sent; the message was not sent.');
MAPI_E_TOO_MANY_FILES:
Showmessage('There were too many file attachments; no message was sent.');
MAPI_E_TOO_MANY_RECIPIENTS:
Showmessage('There were too many recipients; no message was sent.');
MAPI_E_UNKNOWN_RECIPIENT:
Showmessage('A recipient did not appear in the address list; no message was sent.');
MAPI_E_USER_ABORT:
Showmessage('The user canceled the process; no message was sent.');
else
Showmessage('MAPISendMail failed with an unknown error code.');
Result := False;
end;
end;

Answer 1

I can see two obvious mistakes. Firstly you use a lot of implicit temporary AnsiString variables whose lifetime is unclear. This happens whenever you do
PAnsiChar(AnsiString(...))
The compiler makes a temporary AnsiString local variable. You are relying on the compiler making enough of them, one for each distinct string.
When you do this inside a loop, the compiler will have one implicit local variable shared between all iterations. That's not enough. You might get away with this because the memory manager doesn't happen to re-use the memory. But your code is still wrong.
I would create a TList<AnsiString> to hold the numerous AnsiString variables. Every time you need to get a PAnsiChar do this:
astr := AnsiString(...);
TempAnsiStrings.Add(astr);
... := PAnsiChar(astr);
where TempAnsiStrings is your list that holds temporary AnsiString objects. Wrap this up in a nested function for ease of use.
function GetPAnsiChar(const str: string): PAnsiChar;
var
astr: AnsiString;
begin
astr := AnsiString(str);
TempAnsiStrings.Add(astr);
Result := PAnsiChar(astr);
end;
Obviously you need to instantiate the list, and destroy it, but I trust you already know how to do that.
Your other problem are the calls to StrDispose. You have to remove them since the compiler is managing lifetime. Call StrDispose to free memory allocated with StrNew or StrAlloc. You don't allocate this way so there is no place for StrDispose.
Rather than using explicit memory allocation for list of files, a dynamic array would be cleaner. This would have the other benefit of avoiding the possibility of leaking that your code currently has due to its missing finally block.