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</head><body><p style="font-size: 12pt; font-family: helvetica, arial, sans-serif; color: rgb(51, 51, 51);">Mozilla support forum came through:<br></p><p style="font-size: 12pt; font-family: helvetica, arial, sans-serif; color: rgb(51, 51, 51);"><br></p><p style="font-size: 12pt; font-family: helvetica, arial, sans-serif; color: rgb(51, 51, 51);">Terminal command "nslookup imap.comcast.net" yields imap.comcast.net canonical name = imap.ge.xfinity.com.<br></p><p style="font-size: 12pt; font-family: helvetica, arial, sans-serif; color: rgb(51, 51, 51);"><br></p><p style="font-size: 12pt; font-family: helvetica, arial, sans-serif; color: rgb(51, 51, 51);">Substituting imap.ge.xfinity.com for imap.comcast.net in the Thunderbird email account "manual setup" window works properly as it should.<br></p><p style="font-size: 12pt; font-family: helvetica, arial, sans-serif; color: rgb(51, 51, 51);"><br></p><p style="font-size: 12pt; font-family: helvetica, arial, sans-serif; color: rgb(51, 51, 51);">Hopefully I'll achieve similar results with Kmail and Sylpheed.<br></p></body></html>