Hi Sam,

welcome to Typophile!
Please note that you get faster feedback when you post such ID requests on the Type ID Board.

Postmarks use custom letters, i.e. there is probably no digital font that perfectly matches your sample.

For an approximation of the date (digits): this might be a case for Linotype DIN Next. It has the ‘9’ with the rounded bottom, as an alternative glyph. Neither DIN Engschrift, FF DIN nor PF DIN seem to have this form.
DIN Next has a Condensed, and a Rounded. Alas, no Condensed Rounded.

Alternatively, there’s Gravur Condensed.

Cheers,
F

If the stamped look is of importance, try Linotype Tagesstempel.