Emails not be received

[Pisces]

I am sending emails to my daughter by Outlook Express. I am with Tiscali (TalkTalk) and she is with BT.

Over the last two weeks she has only been receiving a random few emails from me. I am now numbering them so she knows that some are missing.

If I resend them from the 'sent' folder she generally receives them.

I am now sending the original and at the same time 'forwarding' the same email from the 'sent' folder.

She is receiving the 'forwarded' one but still not the original.

Any ideas what can be done to resolve this please. Thank you.