I don't use a modem anymore, but: It seems very unlikely that this is a limitation of linux. You would not be the first one to notice this problem. Does this happen with ftp? What is the error message you are getting? Maybe your ISP doesn't like what your linux modem driver is doing. This link may be interesting:
http://www.linuxdoc.org/HOWTO/Modem-HOWTO-17.html#ss17.4 Joel > Problems sending large attachments? > > I have a P111 notebook with over 300MB memory, using a pcmcia modem running > on Redhat 7.2. I use Kmail 1.3.2 on KDE 2.2.2-1 and Mutt 1.3.25i . I have > used sendmail-8.11.6-3 and have configured Kmail and mutt to use this > > I can send emails with small attachments, receive emails even with large > attachments but when I try to send large attachments around 40 KB and over > using either ./sendmail -v -q or Kmail's smtp server, I get error messages, > and the connection freezes. Mutt sends the mail to mqueue and when I use > sendmail -q the connection stalls. > > This has happened with different desktops, different distros i.e. Redhat and > SuSE 7.3. I have no problem when I use Windows, so it is not the ISP. Could > it be a problem with 'wvdial.conf' or some other configuation file, limiting > the size of message I can send? I have spent alot of time searching for > answers and using different configuration of sendmail but unfortunately > without joy. > > Is this a problem with linux, I need to send large attachments sometimes > from home to work. Do I need to keep Windows installed? > > Jim > > > >
