I went through the zone file by eliminating sections and trying to import it. Finally figured out the section that was giving me the grief. The MX records shown below are exactly as imported from Linode.
@ 3600 MX 1 ASPMX.L.GOOGLE.COM.
@ 3600 MX 5 ALT1.ASPMX.L.GOOGLE.COM.
@ MX 5 ALT2.ASPMX.L.GOOGLE.COM.
@ MX 10 ASPMX2.GOOGLEMAIL.COM.
@ MX 10 ASPMX3.GOOGLEMAIL.COM.
If I remove 3600 from the first two lines, I was able to import the file. Not sure why Linode gives out this file. So MX records now look like this when I import them.
@ MX 1 ASPMX.L.GOOGLE.COM.
@ MX 5 ALT1.ASPMX.L.GOOGLE.COM.
@ MX 5 ALT2.ASPMX.L.GOOGLE.COM.
@ MX 10 ASPMX2.GOOGLEMAIL.COM.
@ MX 10 ASPMX3.GOOGLEMAIL.COM.