In case it helps, here are the results of testssl.sh:
    
jervin@MiniUntu:~/testssl/testssl.sh$ ./testssl.sh
        kumo.kites.org:993
      
      ###########################################################
          testssl.sh       3.0rc5 from https://testssl.sh/dev/
          (35c69be 2019-10-02 17:53:37 -- )
      
            This program is free software. Distribution and
                   modification under GPLv2 permitted.
            USAGE w/o ANY WARRANTY. USE IT AT YOUR OWN RISK!
      
             Please file bugs @ https://testssl.sh/bugs/
      
      ###########################################################
      
       Using "OpenSSL 1.0.2-chacha (1.0.2k-dev)" [~183 ciphers]
       on MiniUntu:./bin/openssl.Linux.x86_64
       (built: "Jan 18 17:12:17 2019", platform:
        "linux-x86_64")
      
      
       Start 2019-10-11 07:28:20        -->>
        3.222.54.62:993 (kumo.kites.org) <<--
      
       rDNS (3.222.54.62):     kumo.kites.org.
       Service detected:       IMAP, thus skipping HTTP
        specific checks
      
      
       Testing protocols via sockets except NPN+ALPN 
      
       SSLv2      not offered (OK)
       SSLv3      not offered (OK)
       TLS 1      offered (deprecated)
       TLS 1.1    offered (deprecated)
       TLS 1.2    offered (OK)
       TLS 1.3    offered (OK): final
       NPN/SPDY   not offered
       ALPN/HTTP2 not offered
      
       Testing cipher categories 
      
       NULL ciphers (no encryption)                  not
        offered (OK)
       Anonymous NULL Ciphers (no authentication)    not
        offered (OK)
       Export ciphers (w/o ADH+NULL)                 not
        offered (OK)
       LOW: 64 Bit + DES, RC[2,4] (w/o export)       not
        offered (OK)
       Triple DES Ciphers / IDEA                     not
        offered (OK)
       Average: SEED + 128+256 Bit CBC ciphers       offered
       Strong encryption (AEAD ciphers)              offered
        (OK)
      
      
       Testing robust (perfect) forward secrecy, (P)FS --
        omitting Null Authentication/Encryption, 3DES, RC4 
      
       PFS is offered (OK)          TLS_AES_256_GCM_SHA384
        TLS_CHACHA20_POLY1305_SHA256
                                    ECDHE-RSA-AES256-GCM-SHA384
        ECDHE-RSA-AES256-SHA384 ECDHE-RSA-AES256-SHA
                                    DHE-RSA-AES256-GCM-SHA384
        ECDHE-RSA-CHACHA20-POLY1305
                                    DHE-RSA-CHACHA20-POLY1305
        DHE-RSA-AES256-CCM8 DHE-RSA-AES256-CCM
                                    DHE-RSA-AES256-SHA256
        DHE-RSA-AES256-SHA ECDHE-RSA-CAMELLIA256-SHA384
                                    DHE-RSA-CAMELLIA256-SHA256
        DHE-RSA-CAMELLIA256-SHA
                                    DHE-RSA-ARIA256-GCM-SHA384
        ECDHE-ARIA256-GCM-SHA384
                                    TLS_AES_128_GCM_SHA256
        ECDHE-RSA-AES128-GCM-SHA256
                                    ECDHE-RSA-AES128-SHA256
        ECDHE-RSA-AES128-SHA DHE-RSA-AES128-GCM-SHA256
                                    DHE-RSA-AES128-CCM8
        DHE-RSA-AES128-CCM DHE-RSA-AES128-SHA256
                                    DHE-RSA-AES128-SHA
        ECDHE-RSA-CAMELLIA128-SHA256
                                    DHE-RSA-CAMELLIA128-SHA256
        DHE-RSA-SEED-SHA DHE-RSA-CAMELLIA128-SHA
                                    DHE-RSA-ARIA128-GCM-SHA256
        ECDHE-ARIA128-GCM-SHA256 
       Elliptic curves offered:     secp384r1 
       DH group offered:            Unknown DH group (1024
        bits)
      
       Testing server preferences 
      
       Has server cipher order?     yes (OK) -- only for <
        TLS 1.3
       Negotiated protocol          TLSv1.3
       Negotiated cipher            TLS_AES_256_GCM_SHA384, 384
        bit ECDH (P-384)
       Cipher order
          TLSv1:     ECDHE-RSA-AES256-SHA DHE-RSA-AES256-SHA
        DHE-RSA-CAMELLIA256-SHA AES256-SHA
                     CAMELLIA256-SHA ECDHE-RSA-AES128-SHA
        DHE-RSA-AES128-SHA DHE-RSA-SEED-SHA
                     DHE-RSA-CAMELLIA128-SHA AES128-SHA
        SEED-SHA CAMELLIA128-SHA 
          TLSv1.1:   ECDHE-RSA-AES256-SHA DHE-RSA-AES256-SHA
        DHE-RSA-CAMELLIA256-SHA AES256-SHA
                     CAMELLIA256-SHA ECDHE-RSA-AES128-SHA
        DHE-RSA-AES128-SHA DHE-RSA-SEED-SHA
                     DHE-RSA-CAMELLIA128-SHA AES128-SHA
        SEED-SHA CAMELLIA128-SHA 
          TLSv1.2:   ECDHE-RSA-AES256-GCM-SHA384
        ECDHE-RSA-AES256-SHA384 ECDHE-RSA-AES256-SHA
                     DHE-RSA-AES256-GCM-SHA384
        ECDHE-RSA-CHACHA20-POLY1305 DHE-RSA-CHACHA20-POLY1305
                     DHE-RSA-AES256-CCM8 DHE-RSA-AES256-CCM
        DHE-RSA-AES256-SHA256 DHE-RSA-AES256-SHA
                     ECDHE-RSA-CAMELLIA256-SHA384
        DHE-RSA-CAMELLIA256-SHA256 DHE-RSA-CAMELLIA256-SHA
                     AES256-GCM-SHA384 AES256-CCM8 AES256-CCM
        AES256-SHA256 AES256-SHA CAMELLIA256-SHA256
                     CAMELLIA256-SHA ARIA256-GCM-SHA384
        DHE-RSA-ARIA256-GCM-SHA384 ECDHE-ARIA256-GCM-SHA384
                     ECDHE-RSA-AES128-GCM-SHA256
        ECDHE-RSA-AES128-SHA256 ECDHE-RSA-AES128-SHA
                     DHE-RSA-AES128-GCM-SHA256
        DHE-RSA-AES128-CCM8 DHE-RSA-AES128-CCM AES128-CCM8 AES128-CCM
                     DHE-RSA-AES128-SHA256 DHE-RSA-AES128-SHA
        ECDHE-RSA-CAMELLIA128-SHA256
                     DHE-RSA-CAMELLIA128-SHA256
        DHE-RSA-SEED-SHA DHE-RSA-CAMELLIA128-SHA AES128-GCM-SHA256
                     AES128-SHA256 AES128-SHA
        CAMELLIA128-SHA256 SEED-SHA CAMELLIA128-SHA ARIA128-GCM-SHA256
                     DHE-RSA-ARIA128-GCM-SHA256
        ECDHE-ARIA128-GCM-SHA256 
          TLSv1.3:   TLS_AES_256_GCM_SHA384
        TLS_CHACHA20_POLY1305_SHA256 TLS_AES_128_GCM_SHA256 
      
      
       Testing server defaults (Server Hello) 
      
       TLS extensions (standard)    "renegotiation info/#65281"
        "server name/#0" "EC point formats/#11"
                                    "session ticket/#35"
        "supported versions/#43" "key share/#51"
                                    "max fragment length/#1"
        "encrypt-then-mac/#22"
                                    "extended master
        secret/#23"
       Session Ticket RFC 5077 hint 7200 seconds, session
        tickets keys seems to be rotated < daily
       SSL Session ID support       yes
       Session Resumption           Tickets no, ID: no
       TLS clock skew               Random values, no
        fingerprinting possible 
       Signature Algorithm          SHA256 with RSA
       Server key size              RSA 2048 bits
       Server key usage             Digital Signature, Key
        Encipherment
       Server extended key usage    TLS Web Server
        Authentication, TLS Web Client Authentication
       Serial / Fingerprints       
        F451FC38110BD0CC08D03E6975C05AC0 / SHA1
        5EB402C1FB4020C1697E48931F68D11145D48F43
                                    SHA256
        C37816C37E38DAEF4758EC41EA9F332C08C9310CA63976BD5A294EE7D84B3CF0
       Common Name (CN)             kumo.kites.org
       subjectAltName (SAN)         kumo.kites.org
        www.kumo.kites.org 
       Issuer                       Sectigo RSA Domain
        Validation Secure Server CA (Sectigo Limited from GB)
       Trust (hostname)             Ok via SAN and CN (same w/o
        SNI)
       Chain of trust               Ok   
       EV cert (experimental)       no 
       ETS/"eTLS", visibility info  not present
       Certificate Validity (UTC)   364 >= 60 days
        (2019-10-10 20:00 --> 2020-10-09 19:59)
       # of certificates provided   6 (certificate list
        ordering problem)
       Certificate Revocation List  --
       OCSP URI                     http://ocsp.sectigo.com
       OCSP stapling                not offered
       OCSP must staple extension   --
       DNS CAA RR (experimental)    not offered
       Certificate Transparency     yes (certificate extension)
      
      
       Testing vulnerabilities 
      
       Heartbleed (CVE-2014-0160)                not vulnerable
        (OK), no heartbeat extension
       CCS (CVE-2014-0224)                       not vulnerable
        (OK)
       Ticketbleed (CVE-2016-9244), experiment.  --  
        (applicable only for HTTPS)
       ROBOT                                     not vulnerable
        (OK)
       Secure Renegotiation (RFC 5746)           supported (OK)
       Secure Client-Initiated Renegotiation     not vulnerable
        (OK)
       CRIME, TLS (CVE-2012-4929)                not vulnerable
        (OK) (not using HTTP anyway)
       POODLE, SSL (CVE-2014-3566)               not vulnerable
        (OK)
       TLS_FALLBACK_SCSV (RFC 7507)              Downgrade
        attack prevention supported (OK)
       SWEET32 (CVE-2016-2183, CVE-2016-6329)    not vulnerable
        (OK)
       FREAK (CVE-2015-0204)                     not vulnerable
        (OK)
       DROWN (CVE-2016-0800, CVE-2016-0703)      not vulnerable
        on this host and port (OK)
                                                 make sure you
        don't use this certificate elsewhere with SSLv2 enabled services
                                                
https://censys.io/ipv4?q=C37816C37E38DAEF4758EC41EA9F332C08C9310CA63976BD5A294EE7D84B3CF0
        could help you to find out
       LOGJAM (CVE-2015-4000), experimental      not vulnerable
        (OK): no DH EXPORT ciphers
                                                 But: Unknown
        DH group (1024 bits)
       BEAST (CVE-2011-3389)                     TLS1:
        ECDHE-RSA-AES256-SHA DHE-RSA-AES256-SHA
                                                      
        DHE-RSA-CAMELLIA256-SHA AES256-SHA CAMELLIA256-SHA
                                                      
        ECDHE-RSA-AES128-SHA DHE-RSA-AES128-SHA
                                                      
        DHE-RSA-SEED-SHA DHE-RSA-CAMELLIA128-SHA AES128-SHA
                                                       SEED-SHA
        CAMELLIA128-SHA 
                                                 VULNERABLE --
        but also supports higher protocols  TLSv1.1 TLSv1.2 (likely
        mitigated)
       LUCKY13 (CVE-2013-0169), experimental     potentially
        VULNERABLE, uses cipher block chaining (CBC) ciphers with TLS.
        Check patches
       RC4 (CVE-2013-2566, CVE-2015-2808)        no RC4 ciphers
        detected (OK)
      
      
       Testing 370 ciphers via OpenSSL plus sockets against the
        server, ordered by encryption strength 
      
      Hexcode  Cipher Suite Name (OpenSSL)       KeyExch.  
        Encryption  Bits     Cipher Suite Name (IANA/RFC)
      -----------------------------------------------------------------------------------------------------------------------------
      [redacted to reduce size]
      
      
       Running client simulations via sockets 
      
       Android 8.1 (native)         TLSv1.2
        ECDHE-RSA-AES128-GCM-SHA256, 384 bit ECDH (P-384)
       Android 9.0 (native)         TLSv1.3
        TLS_AES_128_GCM_SHA256, 384 bit ECDH (P-384)
       Java 6u45                    TLSv1.0 AES128-SHA, No FS
       Java 7u25                    TLSv1.0
        ECDHE-RSA-AES128-SHA, 384 bit ECDH (P-384)
       Java 8u161                   TLSv1.2
        ECDHE-RSA-AES256-SHA384, 384 bit ECDH (P-384)
       Java 11.0.2 (OpenJDK)        TLSv1.3
        TLS_AES_128_GCM_SHA256, 384 bit ECDH (P-384)
       Java 12.0.1 (OpenJDK)        TLSv1.3
        TLS_AES_128_GCM_SHA256, 384 bit ECDH (P-384)
       OpenSSL 1.0.1l               TLSv1.2
        ECDHE-RSA-AES256-GCM-SHA384, 384 bit ECDH (P-384)
       OpenSSL 1.0.2e               TLSv1.2
        ECDHE-RSA-AES256-GCM-SHA384, 384 bit ECDH (P-384)
       OpenSSL 1.1.0j (Debian)      TLSv1.2
        ECDHE-RSA-AES256-GCM-SHA384, 384 bit ECDH (P-384)
       OpenSSL 1.1.1b (Debian)      TLSv1.3
        TLS_AES_256_GCM_SHA384, 384 bit ECDH (P-384)
       Thunderbird (60.6)           TLSv1.3
        TLS_AES_128_GCM_SHA256, 384 bit ECDH (P-384)
      
       Done 2019-10-11 07:31:08 [ 170s] -->>
        3.222.54.62:993 (kumo.kites.org) <<--
      
      
    
In setting up my new mail server, I am getting the following in the logs:
Oct 11 07:10:59 kumo dovecot[5704]: imap-login: Disconnected (no auth attempts in 0 secs): user=<>, rip=24.53.79.10, lip=172.26.12.90, TLS handshaking: SSL_accept() syscall failed: Success, session=<B9OokqCUD+UYNU8K>