Genicom GEK 00031B Programmer's Manual page 267

Restrictions
Printer option strap 13 in General Printer Options, paper position
reset to top of bar code after printing, is ignored while using
POSTNET. (See Appendix D, General Printer Options, Group 2).
If the symbol exceeds the right margin, the symbol is cut off at the
margin.
POSTNET codes cannot be used on the same line as the high speed
font.
Exit the bar code mode before sending other control codes or escape
sequences.
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GEK-00029B 5000 Series Programmer's Manual