random email sent from a pop account to exchange account go missing

Random emails sent using Outlook 2007 and a pop account go missing and never showup anywhere or get no Bouce Back messages.
eg: email from lb@sddf.com (pop-Outlook2007) to warehouse@isppes.com (exchange 2007) account go missing
while people cced on the same email eg: nbhate@isppes.com get the email
When the cced person reply to the email the original sender lb@sddf.com doesnt get the email
Spoke with the POP hosting account provider and they had us check the email using webmail and mostly they went through, so didnt get much help from there.
Checked on the MXToolbox - results came clean
Please help
Nilam BhateAsked:
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David Johnson, CD, MVPOwnerCommented:
When the cced person reply to the email the original sender lb@sddf.com doesn't get the email
That would imply that the reply-to setting is incorrect in the original message sent from lb@sddf
Either fix it or remove it.
Nilam BhateAuthor Commented:
We did some further tests and found that the Outlook was NOT submitting the email to the POP server.
- We sent a email from lb@sddf.com (outlook 2007) to lb@sddf.com and kept an eye on the webmail to see if this email would appear there - and we found that it never reached there.
- we then used webmail of lb@sddf.com to sent email to lb@sddf.com - this time it appeared promptly
So my deduction is that Outlook is randomly not submitting the emails.
Secondly as David Johnson, MVP suggests the reply to settings are incorrect which cause other issues.

Can anyone suggest how we can test the outlok 2007 to be sure that it is not holding emails back ?

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can you tell me are you sending test emails to this id or sending some attachments.
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David Johnson, CD, MVPOwnerCommented:
did you ensure that the account is set properly? can outlook send the test email? in the account settings?
Nilam BhateAuthor Commented:
The account settings are fine, checked over and over again
tests are successful each time and we can see the test emails
Nilam BhateAuthor Commented:
Best course of action so far
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