What to do when Gmail won't accept self-signed SSL certificates
Why Can’t I Download Google Messages?
Google Mail, also known as Gmail, stopped accepting self-signed certificates as a security measure. Anyone using self signed certificates for SSL email applications are now unable to transfer their emails to the Google Mail service, Gmail.
How then do you download your Google Mail / Gmail messages now that Google will not let you download email to a server with self signed certificates?
Root Cause of the Issue
When Google Mail (Gmail) downloads emails from another server, it uses the POP protocol. The Secure Sockets Layer (SSL) is an encryption layer over that to secure your information from interception. To establish an SSL connection with the server requires a certificate (from the server) that allows you to decrypt the data.
This certificate can be purchased from a trusted third-party (for commercial applications), or a self-signed certificate is frequently used for small local applications. Once the end user has accepted the self-signed certificate, then it works correctly. (Third party trusted certificates do not give users any warning messages.)
Google changed their policy wiithout any advance notice so that the Gmail servers will not allow any self-signed certificates. Nor is Google likely to change this policy, since the change is rooted in security concerns.
Several Solutions to Download Email from a Private Server to Google Mail or Gmail
1) Register a formal domain, and purchase an annual signed certificate. Then use POP to download email to the private server with a signed certificate to Gmail.
2) Redirect email thru non-Google providers. The non-Google providers may still accept the self-signed certificates.
3) Use non-secure POP that sends username and password in plain text. However, this is not recommended due to the security risk it poses.
Fundamentals of SSL and Email Communications – and the Risks Drove Google to Make These Changes
To receive your emails from the server, you POP them. You are taking the messages and copying them down from the server. Some computer configurations use IMAP, but that is secondary to this discussion.
SMTP is what sends the email from your machine to the email server. From a user’s perspective, POP downloads the messages from the email server while SMTP is to upload messages to the server to be sent.
Historically, the POP and SMTP protocols were built in an insecure way. A lot of the information was transferred in text. Encryption came later to make these protocols secure. This is done with wrappers to secure these connections.
One of the most common encryption methods used is SSL, the Secure Sockets Layer. SSL is just an encryption method that creates an encrypted connection. Then you can transfer the data back and forth for sending and receiving messages.
As a user, every time you contact the POP or SMTP server, you must supply your user name and password to access the information. This tells the server which messages to upload or download and verifies the user’s access to the information. The user name and password used to be sent as unsecured text.
The SSL protocol requires a certificate for encryption purposes. That certificate authenticates the server and prevents someone else from interjecting their data in your data stream. The certificate can be purchased from a third party like Verisign.
Another option has been self-signed certificates, which users could authorize themselves. This works best for small and private servers. It was also free, compared to the annual signed SSL certificates available through several certification authorities. However, anyone could create a self-signed SSL certificate, which is why it was deemed a security risk by Google.
The security risk posed by failing to use SSL and encryption exist despite the Heartbleed encryption exploit.