Adding ProtonMail Account to Mailspring Fails w/Certificate Error

I’m running Feren OS 2021.07. I successively installed ProtonMail Bridge and signed in using my ProtonMail account. When I try to add my ProtonMail account to Mailspring, using the settings provided by the ProtonMail Bridge for my account, I receive a “Certificate Error (SMTP)”. The verification error log reports:

OpenSSL version: OpenSSL 1.1.0f 25 May 2017
Verification failed:

X509 verify_cert_error_string:

self signed certificate


My system stores certificates at:

Did you check “Allow insecure SSL”?