smtp.office365.com – Failed to get initial SMTP Response

If something on the client-side is blocking communications, such as a hardware or software firewall, or anti-virus, then it may be that a TLS connection is established, but then trying to read the 1st message from the server gets blocked.  When this happens, the contents of the LastErrorText look like this.   (The LastErrorText for a successful connection is shown below.)

Firewall or Anti-Virus Blocking Communications:

        ensureSmtpSession(62172ms):
          ensureSmtpConnection(62172ms):
            smtpParams:
              SmtpHost: smtp.office365.com
              SmtpPort: 587
              SmtpUsername: joe@example.com
              SmtpSsl: 0
              StartTLS: 1
            --smtpParams
            smtpConnect(62172ms):
              smtpHostname: smtp.office365.com
              smtpPort: 587
              connectionIsReady:
                Need new SMTP connection
              --connectionIsReady
              smtpSocketConnect(109ms):
                socket2Connect(109ms):
                  connect2(109ms):
                    hostname: smtp.office365.com
                    port: 587
                    ssl: False
                    connectSocket(109ms):
                      domainOrIpAddress: smtp.office365.com
                      port: 587
                      connectTimeoutMs: 30000
                      connect_ipv6_or_ipv4(109ms):
                        Multi-threaded domain to IP address resolution
                        resolveHostname6(15ms):
                          maxTimeMs: 30000
                        --resolveHostname6
                        connecting to IPV4 address...
                        ipAddress: 111.111.111.111
                        createSocket:
                          Setting SO_SNDBUF size
                          sendBufSize: 262144
                          Setting SO_RCVBUF size
                          recvBufSize: 4194304
                        --createSocket
                        connect(94ms):
                          Waiting for the connect to complete...
                          connectTimeoutMs: 30000
                          myIP: 10.225.229.198
                          myPort: 61274
                          socket connect successful.
                        --connect
                      --connect_ipv6_or_ipv4
                    --connectSocket
                  --connect2
                --socket2Connect
                Turning on TCP_NODELAY.
                socketOptions:
                  SO_SNDBUF: 262144
                  SO_RCVBUF: 4194304
                  TCP_NODELAY: 1
                  SO_KEEPALIVE: 1
                --socketOptions
              --smtpSocketConnect
              smtpGreeting(30938ms):
                readSmtpResponse(30938ms):
                  idleTimeoutMs: 30000
                --readSmtpResponse
              --smtpGreeting
              Failed to get initial SMTP response..

Nothing is Blocking Communications:

        ensureSmtpSession(2000ms):
          ensureSmtpConnection(219ms):
            smtpParams:
              SmtpHost: smtp.office365.com
              SmtpPort: 587
              SmtpUsername: joe@example.com
              SmtpSsl: 0
              StartTLS: 1
            --smtpParams
            smtpConnect(219ms):
              smtpHostname: smtp.office365.com
              smtpPort: 587
              smtpSocketConnect(47ms):
                socket2Connect(47ms):
                  connect2(47ms):
                    hostname: smtp.office365.com
                    port: 587
                    ssl: False
                    connectSocket(47ms):
                      domainOrIpAddress: smtp.office365.com
                      port: 587
                      connectTimeoutMs: 30000
                      connect_ipv6_or_ipv4(47ms):
                        Multi-threaded domain to IP address resolution
                        resolveHostname6(31ms):
                          maxTimeMs: 30000
                        --resolveHostname6
                        connecting to IPV4 address...
                        ipAddress: 111.111.111.111
                        createSocket:
                          Setting SO_SNDBUF size
                          sendBufSize: 262144
                          Setting SO_RCVBUF size
                          recvBufSize: 4194304
                        --createSocket
                        connect(16ms):
                          Waiting for the connect to complete...
                          connectTimeoutMs: 30000
                          myIP: 172.16.16.23
                          myPort: 55842
                          socket connect successful.
                        --connect
                      --connect_ipv6_or_ipv4
                    --connectSocket
                  --connect2
                --socket2Connect
                Turning on TCP_NODELAY.
                socketOptions:
                  SO_SNDBUF: 262144
                  SO_RCVBUF: 4194304
                  TCP_NODELAY: 1
                  SO_KEEPALIVE: 1
                --socketOptions
              --smtpSocketConnect
              smtpGreeting(31ms):
                readSmtpResponse(31ms):
                  SmtpCmdResp: 220 CH0PR07CA0022.outlook.office365.com Microsoft ESMTP MAIL Service ready at Fri, 13 May 2022 12:49:13 +0000
                  smtpStatusCode: 220
                --readSmtpResponse
              --smtpGreeting