I have installed the bionic-proposed updates and worked for imap connections to imap.mail.yahoo.com on port 993.
Updated the next packages with Synaptic:
libgnutls-openssl27 (3.5.18-1ubuntu1.3) to 3.5.18-1ubuntu1.4
libgnutls30 (3.5.18-1ubuntu1.3) to 3.5.18-1ubuntu1.4
libgnutls30:i386 (3.5.18-1ubuntu1.3) to 3.5.18-1ubuntu1.4
I have installed the bionic-proposed updates and worked for imap connections to imap.mail.yahoo.com on port 993.
Updated the next packages with Synaptic:
libgnutls-openssl27 (3.5.18-1ubuntu1.3) to 3.5.18-1ubuntu1.4
libgnutls30 (3.5.18-1ubuntu1.3) to 3.5.18-1ubuntu1.4
libgnutls30:i386 (3.5.18-1ubuntu1.3) to 3.5.18-1ubuntu1.4
Thanks a lot for your work!