[Users] SNI and Google Mail self-signed certificate for IMAP

[Michael Schwendt]

Both Claws Mail 3.16.0 and 3.17.1, which don't exhibit the same
symptoms on Fedora 28, on Fedora 29 only get offered a self-signed
certificate when contacting Google Mail IMAP using gnutls.

It is not clear to me yet what exactly has changed and whether
the theory that it is related to SNI is correct. Why would the same
package be affected only on F29 and not F28?

Is anything known about this yet?

$ strings ~/.claws-mail/certs/imap.gmail.com.993.cert
0N110/
(No SNI provided; please fix your client.1
invalid2.invalid0
150101000000Z
300101000000Z0N110/
(No SNI provided; please fix your client.1
invalid2.invalid0
}	\Y
	w[M
]0[0
0*`d
#vBc
?I_n