flat file line breaks lost via unix mail

Question

I have a flat file with lines of data. When I pipe it through /bin/mail to myself, however, the text in my MS Outlook mail box will have certain lines next to each other (EOL lost). For example, the file has

... 
20100115  0.48856  0.53141  0.36264  0.36237
20100119  0.48047  0.53160  0.36643  0.36516 
20100120  0.48551  0.53396  0.36970  0.36690
20100121  0.53207  0.55707  0.38302  0.37606
....

and if I run cat data.txt | mail my.name@myfirm.com, I see

... 
20100115  0.48856  0.53141  0.36264  0.36237
20100119  0.48047  0.53160  0.36643  0.36516 20100120  0.48551  0.53396  0.36970  0.36690
20100121  0.53207  0.55707  0.38302  0.37606
....

Regardless of if I convert the flat file to unix or dos format, this happens. And it always happens to certain lines but not others. And after some experiment, turns out that if the first word of the next line ends with 0, then this always happens.

Why would that be? Any solution to the problem would be much appreciated.