Office365 POP3 Authenticate Fails but Previously Succeeded

It’s normal for OAuth2 access tokens to expire after some time, such as 1 hour, and then you’ll need to refresh and retry. For example, this error in the LastErrorText for a call to Pop3Authenticate could indicate the OAuth2 accces token expired: Pop3Authenticate: DllDate: Mar 28 2023 ChilkatVersion: UnlockPrefix: *** Architecture: Little Endian; 32-bit Language: ActiveX VerboseLogging: 1 Pop3Authenticate: […]

Office365 Modern Authentication for IMAP, POP3, and SMTP

This post documents how to implement Modern Authentication (OAuth2) for Office365 for the IMAP, POP3, and SMTP protocols.  The very first thing you’ll need to do is to create an “App Registration” in Azure Active Directory. See this Chilkat blog post for Instructions for Setting Up an App Registration in Azure for Modern Authentication for IMAP, SMTP, and POP3. It’s […]

Create Azure App Registration for use with IMAP, POP3, and SMTP

1) Go to and login to your Microsoft account. then go to Azure Active Directory.   2) Click On App Registrations * Copy your Tenant ID, you’ll need it later. 3) Click on “+ New registration” 4) Name your App and Click Register. Give it a name. For the Redirect URI, select “Web” and then use “http://localhost:3017/”. Your application […]

POP3 Error: No X-UIDL header found

The Chilkat MailMan class can fetch emails from a POP3 server in two ways: by sequence number, or by UIDL. When an email is fetched by UIDL, or fetched in a way such that a full mapping of UIDL’s to sequence numbers was retrieved, Chilkat will add an “X-UIDL” header to the Email object that is returned. This allows for […]

Number of Messages in a POP3 Inbox

There is often confusion about the number of messages in a POP3 inbox (for a given user account). Here are the typical scenarios that cause confusion: If your email client such as Outlook or Mozilla Thunderbird seem to show more messages than what Chilkat can see, then make sure you realize which messages are stored locally by Outlook, and which […]

GMail POP3 Authentication — Must Unlock Captcha

If captcha is enabled on your GMail account (and it is enabled by default), then GMail POP3 authentication will fail with this error (even though a correct login/password is provided) **** Connected to < +OK Gpop ready for requests from c23pf1097242ibu.22 > USER < +OK send PASS > PASS **** < -ERR [AUTH] Username and password not […]

POP3 over HTTP Proxy

ASP: POP3 using HTTP Proxy SQL Server: POP3 using HTTP Proxy C#: POP3 using HTTP Proxy C++: POP3 using HTTP Proxy MFC: POP3 using HTTP Proxy C: POP3 using HTTP Proxy Delphi: POP3 using HTTP Proxy Visual FoxPro: POP3 using HTTP Proxy Java: POP3 using HTTP Proxy Perl: POP3 using HTTP Proxy PHP: POP3 using HTTP Proxy Python: POP3 using […]

Understanding GMail’s Behavior

This blog post will explain GMail in a way that will help you understand it’s seemingly strange behavior. The question that prompted this post is as follows: I am able to read mails from GMail mailbox using MailMan object. Is there any options to delete a mail permanently from GMail mailbox? When I am using the DeleteMail method the mail […]

Exchange Server – POP3, IMAP, and SMTP

Question: May I ask if is possible use Chilkat components to connect to MS Exchange 6.5 and higher ? I am thinking about purchase of MailMan component or other as it is, however I would like read some example in C# for reading emails from Exchange and sending emails via Exchange after connecting to the specified account domain/logname & password. […]