Win7/Livemail

I,ve got a phone(Nokia), tablet (Samsung)and laptop(Asus). Each of the three
can send an email and it gets received by all three normally
but if I send an email with an attachment from the laptop it gets sent ie
you can see "sending email" on screen
but it never arrives on any of the three. An email with attachment gets sent
ok from phone and tablet. I,ve been sending emails with attachments from
this
laptop for last 6 years and all settings appear as they should be.
Any help much appreciated
John

John wrote:


I,ve got a phone(Nokia), tablet (Samsung)and laptop(Asus). Each of the
three can send an email and it gets received by all three normally
but if I send an email with an attachment from the laptop it gets sent
ie you can see "sending email" on screen
but it never arrives on any of the three. An email with attachment gets
sent ok from phone and tablet. I,ve been sending emails with attachments
from this
laptop for last 6 years and all settings appear as they should be.
Any help much appreciated
John

OK, the first test case I'd run, is "ping" the IP address
of the thing the email is sent to (SMTP server???). The ping
response of this server could be turned off.

Some SMTP operators, turn off ICMP on the server as a security
feature. Now, ICMP is used for ping. But it is also used
to handle fragmented packets or something.

Fragmented packet handling is needed, if the MTUs on devices
in the network don't match, and the packet length needs to be
changed before re-transmission.

If the laptop uses a VPN, this can modify the MTU on the interface,
and require fragmented packet handling. Right off hand, I don't
have a ready list of other mechanisms that can change the
functional MTU value.

Also, if you used a VPN, it might look like someone is trying
to use the ISP mail server as a "relay". And that should be
blocked by the routing rules at the ISP.

That's about all the weird stuff I know of, off hand.

*******

You claim this is an attachment problem.

I have another test case you can run. I think the "trigger"
for the problem, is any message longer than 1.5KB.

Craft a message with no attachment. In the message, just
put a line with "my dog has fleas" about 10,000 times, to
pad up the message size. Then see if you can send that.
My guess is, that won't get sent either. When the email
is short enough to fit into a single packet, without
the missing fragmentation support, you'll be able to send it.

If you craft a one-line email message, that's less than 1.5KB
and that will be sent.

*******

It could be your AV program, messing with the mail somehow.

HTH,
Paul