Issue sending email

Please see https://forums.xfinity.com/conversations/email/cant-send-email-from-outlook/65b54a48ed17eb490b580c28?page=3.

Having issues with two email accounts only able to send email between the hours of 5-11P MST.  Accounts are on a CenturyLink network as unable to get Comcast.  Issue persists on both mobile mail clients and Thunderbird mail program on PCs.  Passwords are all good obviously as mail can be sent during the above hours.  Users can log in to Comcast webmail and can send fine.  If the modem is rebooted then the mail will send from either the mobile clients or the PCs for maybe a day then the next day right back to unable to send until the above hours.  I have yet to see a valid fix posted anywhere and it's causing an issue with being able to communicate reliably during the days.