Outgoing email layout deformed

I have created my own MEMO, REPLY and REPLY with history forms. Form has a header with TO,CC,SUBJECT fields (design is done using tables). When I send this form outside our company, the email is received deformed. The width of the table is narrower, therefore the text height is more longer. It doesn’t look nice.

Is there an easy way to fix this?

Or any ideas, how can I design a table, which could be transferred without problems?