Max Terentiev wrote:

> I try to use ICS v6 TWSocket in async non-blocking mode.
> (IDE C++Builder 2007)

You realy should use v7, *v6 is obsolete*, it's not maintained
since 2008. v7 is the successor of v6 and a move should be very easy.
There are more than 600 changes and fixes since v6 in the svn 
repository. Get current source here: 

> Hi,
> After some investigation I have noticed that app slowdown
> happens only if I send large amount of data using TSmtpCli component.

In v7 the send buffer size upon sending file attachments has been
increased, this increased performance a lot, especially with SSL.
However message text is still sent line by line.

> If I try to send large message (2-3 mb) - program hangs until message
> body sent. 

If that happens with a fast network connection (LAN) then it's a
normal behavior in main, GUI thread since paint messages have less 
priority than messages actually posted to the message queue. 
Paint messages are processed only when there are no messages pending
in the queue (on idle), that's why your GUI can freeze.
In such cases you should move the SMTP task into a worker thread
or use the new throttle feature (for an example have a look the
FTP server and demo).   

If it happens with a slow network then I guess your AV or security
software is responsible for the slow down and freeze.

Arno Garrels
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