Marvell 88E8036 Fast Ethernet stops when sending emails with big files attached to it

I have a Marvell 88E8036 Fast Ethernet on my laptop. The network card works fine using the internet and intranet in a regular basis.

There are no problems accesing the web via firefox and sending and receiving emails from thunderbird. The problems comes out when I try to send emails with files over 1MB attached to it.

This problem doesn't appear when you downlod attachments, and I made some tests and i have been able to download attachments over 20MB with no problems at all.

When I send an email with attachments over 1MB (more or less) the process of sending the email starts, showing the progress window as ussual. After certain percentage (not always is the same) the process stops and thunderbird shows the following message:

"Sending of Message Failed

The message could not be sent because connecting to SMTP server server.doamin.com failed. The server mey be unavailable or is refusing SMTP connections. please verify that your SMTP server settings are correct and try again..."

There is not anything diferent from my configuration on windows and works just fine. After this messages you could try several times obtaining the same result, but with different progress percentages in each time.

After this activities, from time to time the ethernet card just stops working and the only way to return back the card to work is ifdown-ing and ifup-ing the interface.

What could be wrong here?. Why in almost all conditions the card behavior is as expected?

Some references about my system:

Toshiba Tecra

Ubuntu Dapper 6.06

uname -a
Linux nilopc 2.6.15-23-386 #1 PREEMPT Tue May 23 13:49:40 UTC 2006 i686 GNU/Linux

ifconfig -a
eth0 Link encap:Ethernet HWaddr 00:A0:D1:BC:AF:78
          inet addr:129.153.210.177 Bcast:129.153.210.255 Mask:255.255.255.0
          inet6 addr: fe80::2a0:d1ff:febc:af78/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
          RX packets:7651 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1087 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:1493201 (1.4 MiB) TX bytes:523622 (511.3 KiB)
          Interrupt:11

lo Link encap:Local Loopback
          inet addr:127.0.0.1 Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING MTU:16436 Metric:1
          RX packets:5 errors:0 dropped:0 overruns:0 frame:0
          TX packets:5 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:272 (272.0 b) TX bytes:272 (272.0 b)