Following a link for an explanation I got:A suspicious app was blocked from accessing your account
The "suspicious app" turned out to be CumulusMX, trying to alert me of an error. I have successfully used the settings below for a long time:To help keep your account secure, starting May 30, 2022, Google will no longer support the use of third-party apps or devices which ask you to sign in to your Google Account using only your username and password.
This is the relevant part from the MXdiags file:
For the next few weeks I can configure Gmail to accept insecure applications, but starting June I will be out of luck. Do I have to change my settings (how?) or does the CumulusMX email module have to be updated/replaced?2022-05-13 06:39:21.690 SendEmail: Error - MailKit.Security.SslHandshakeException: An error occurred while attempting to establish an SSL or TLS connection.
When connecting to an SMTP service, port 587 is typically reserved for plain-text connections. If
you intended to connect to SMTP on the SSL port, try connecting to port 465 instead. Otherwise,
if you intended to use STARTTLS, make sure to use the following code:
client.Connect ("smtp.gmail.com", 587, SecureSocketOptions.StartTls);
---> System.Security.Authentication.AuthenticationException: Authentication failed, see inner exception. ---> Mono.Btls.MonoBtlsException: Ssl error:100000f7:SSL routines:OPENSSL_internal:WRONG_VERSION_NUMBER
at /build/mono-2liaiA/mono-5.18.0.240+dfsg/external/boringssl/ssl/tls_record.c:217
at Mono.Btls.MonoBtlsContext.ProcessHandshake () [0x00054] in <a9a08e39ba304bd0a84c49bd158dfc02>:0
at Mono.Net.Security.MobileAuthenticatedStream.ProcessHandshake (Mono.Net.Security.AsyncOperationStatus status, System.Boolean renegotiate) [0x000c6] in <a9a08e39ba304bd0a84c49bd158dfc02>:0
at (wrapper remoting-invoke-with-check) Mono.Net.Security.MobileAuthenticatedStream.ProcessHandshake(Mono.Net.Security.AsyncOperationStatus,bool)
at Mono.Net.Security.AsyncHandshakeRequest.Run (Mono.Net.Security.AsyncOperationStatus status) [0x00006] in <a9a08e39ba304bd0a84c49bd158dfc02>:0
at Mono.Net.Security.AsyncProtocolRequest.ProcessOperation (System.Threading.CancellationToken cancellationToken) [0x0012a] in <a9a08e39ba304bd0a84c49bd158dfc02>:0
at Mono.Net.Security.AsyncProtocolRequest.StartOperation (System.Threading.CancellationToken cancellationToken) [0x000a4] in <a9a08e39ba304bd0a84c49bd158dfc02>:0
--- End of inner exception stack trace ---
at Mono.Net.Security.MobileAuthenticatedStream.ProcessAuthentication (System.Boolean runSynchronously, Mono.Net.Security.MonoSslAuthenticationOptions options, System.Threading.CancellationToken cancellationToken) [0x00336] in <a9a08e39ba304bd0a84c49bd158dfc02>:0
--- End of inner exception stack trace ---
at MailKit.Net.Smtp.SmtpClient.ConnectAsync (System.String host, System.Int32 port, MailKit.Security.SecureSocketOptions options, System.Boolean doAsync, System.Threading.CancellationToken cancellationToken) [0x002a3] in <eabb09d1c9ea4e16807c3441ccbaf11a>:0
at MailKit.Net.Smtp.SmtpClient.Connect (System.String host, System.Int32 port, MailKit.Security.SecureSocketOptions options, System.Threading.CancellationToken cancellationToken) [0x00012] in <eabb09d1c9ea4e16807c3441ccbaf11a>:0
at CumulusMX.EmailSender.SendTestEmail (System.String[] to, System.String from, System.String subject, System.String message, System.Boolean isHTML) [0x0011e] in <97834895e3104302abf6a91184c2a0c5>:0