This is a weird issue. Intermittently, I losing a network access to the imap-mail,dynu.com server.
My route table is fine and I have disabled and enabled my network card which does not fix the issue. The only resolution is to reboot my pc.

eg: working
c:\ping imap-mail.dynu.com
PING imap-mail.dynu.com (142.202.188.21) 56(84) bytes of data.
64 bytes from imap.dynu.com (142.202.188.21): icmp_seq=1 ttl=48 time=66.4 ms

C:\Windows\System32>tracert imap-mail.dynu.com
Tracing route to imap-mail.dynu.com [142.202.188.21]
over a maximum of 30 hops:
1 <1 ms <1 ms <1 ms jsb-fw1.workgroup [192.168.0.2]
2 8 ms 8 ms 7 ms imap.dynu.com [142.202.188.21]

eg:not working
C:\Windows\System32>ping imap-mail.dynu.com
Pinging imap-mail.dynu.com [142.202.188.21] with 32 bytes of data:
General failure.
General failure.
General failure.
General failure.

C:\Windows\System32>tracert imap-mail.dynu.com
Tracing route to imap-mail.dynu.com [142.202.188.21]
over a maximum of 30 hops:
1 General failure.

route table info:
C:\Windows\System32>route print
===========================================================================
Interface List
9...........................Wintun Userspace Tunnel
13...04 d9 f5 d4 2a 2a ......Realtek Gaming GbE Family Controller
5...00 ff 50 47 c4 1d ......TAP-Windows Adapter V9
1...........................Software Loopback Interface 1
===========================================================================

IPv4 Route Table
===========================================================================
Active Routes:
Network Destination Netmask Gateway Interface Metric
0.0.0.0 0.0.0.0 192.168.0.2 192.168.0.103 25
127.0.0.0 255.0.0.0 On-link 127.0.0.1 331
127.0.0.1 255.255.255.255 On-link 127.0.0.1 331
127.255.255.255 255.255.255.255 On-link 127.0.0.1 331
192.168.0.0 255.255.255.0 On-link 192.168.0.103 281
192.168.0.103 255.255.255.255 On-link 192.168.0.103 281
192.168.0.255 255.255.255.255 On-link 192.168.0.103 281
224.0.0.0 240.0.0.0 On-link 127.0.0.1 331
224.0.0.0 240.0.0.0 On-link 192.168.0.103 281
255.255.255.255 255.255.255.255 On-link 127.0.0.1 331
255.255.255.255 255.255.255.255 On-link 192.168.0.103 281
===========================================================================
Persistent Routes:
None

IPv6 Route Table
===========================================================================
Active Routes:
If Metric Network Destination Gateway
1 331 ::1/128 On-link
13 281 fe80::/64 On-link
13 281 fe80::35e8:24a6:7f4:6f23/128
On-link
1 331 ff00::/8 On-link
13 281 ff00::/8 On-link
===========================================================================
Persistent Routes:
None