GMail is not a normal POP3 server. This blog post explores the oddities of GMail to help you understand what the heck is going on…
To experiment, I have a GMail account (firstname.lastname@example.org), and two email clients setup to read it - Outlook 2003 and Mozilla Thunderbird.
First, I’ll get to a known state.
I’m going to "delete" all of the GMail account emails displayed in Outlook and Thunderbird. Here’s the first GMail oddity: The emails are not really deleted. They still exist on the GMail server. In fact, there is no way to delete email from the GMail server via the POP3 protocol. The only way to delete GMail email is by using the GMail interface interactively.
Next, I go to the "Forwarding and POP" GMail settings and select "Enable POP for all mail (even mail that’s already been downloaded)" and then click the "Save Changes" button.
Now I’m ready to begin experimenting. I download my GMail email in Outlook 2003. Everything looks normal, and I get my email. I go to Mozilla Thunderbird and do the same. However, there are no emails! I go back to my GMail account (via the web browser) and all the emails are still there. Why didn’t the 2nd email client (Thunderbird) see them??? It’s because when the emails were downloaded, Gmail noted it and subsequent POP3 accesses will only return emails that have arrived since the last POP3 access. If you go back to your GMail settings page (make sure you refresh it), you’ll see that the "POP Status" has been updated to read "POP is enabled for all mail that has arrived since 2:25 pm". (The date/time is that of the last POP3 access. ) If you re-select "Enable POP for all mail (even mail that’s already been downloaded)" and click "Save Changes", your next POP3 access will copy all the emails. However, your POP status is automatically updated and the next POP3 access will only get new emails.
To summarize: Accessing emails via POP3 hides those emails from the next POP3 access. For example, if download your new GMail messages onto your laptop (leaving them on the GMail server), you won’t see those messages in Outlook on another computer unless you first log onto Gmail and reset your POP settings. The Chilkat Mail component is a POP3 client just like Outlook or Mozilla Thunderbird, so accessing your GMail programmatically using Chilkat will affect what Outlook sees, and vica-versa (even though the messages are still on the server).
Gmail is great, isn’t it?
Also, you can delete email from the GMail server, but in a non-standard way. If you select "When messages are accessed with POP delete GMail’s copy", then email downloaded via POP3 will be automatically deleted from the server. This is not normal behavior for a POP3 server, which requires an explicit "DELE" command to delete email.