Mail being blocked from 5:00 PM to 7:00 AM - Error CXCNCT
Starting around June 2, 2020 I noticed I was not getting email from my sister if she sent it after 5:00 PM my time (Arizona). Her mail isn’t delivered until about 7:00 AM the next day. My sister has her own mail server to which I have access. The significant entry in her mail server logs during these outages is:
SMTP<< 421 cxr-ibgw-6005a.stratus.cloudmark.com cmsmtp 126.96.36.199 blocked. Refer to Error Codes section at www.cox.com/.../email-error-codes.html for more information. AUP#CXCNCT
The description for the error CXCNCT is “There was a connection issue from the IP address” and the Resolution reads, “There is a limit to the number of concurrent SMTP connections per IP address to protect the systems against attack. Ensure that the sending email server is not opening more than 10 concurrent connections to avoid reaching this limit.”
This resolution is no help. There is no reason to think my sister’s mail server is opening more than 10 concurrent connections. Nothing on her sever was changed on June 2, 2020 and certainly there is no different in the operation of the mail server between 5:00 PM and 7:00 AM.
Although probably not relevant I’ve done the follow to try to figure out or fix this problem.
- I check the mail server reputation and it is neutral
- I check the mail servers IP for being on a blacklist and it is not on any
- I deleted all filtered on my account
- I’ve check my data usage and it is well below the 1024 GB limit.
How can I resolve this issue?