Seriously? I have a 7 in my address as well (and a few 1s), and I receive lots and lots of cards with uncrossed 7s without problems all the time.
I find it incredibly hard not to cross my 7s - I learned it like that at school and it’s really deeply ingrained in my muscle memory.
My 1 is a l and again I find it hard to write it with an upstroke. I sometimes try, but then it always looks super weird to me. 
I always cross my sevens, but nobody else in my family does. I don’t think we learn to write them any specific way in school here, but I think most people I know don’t cross their sevens. I also write my ones with both the half hat and the base.
My eircode/postcode has both a 1 and a 7 and the post gets here no matter which way the numbers are written.
I cross my 7’s and my z’s so neither can be mistaken for a 1 or a 2. Of course my 1 and my capital I are both just a single line sooo
I honestly don’t think about it too much…or at all. I think if someone is working for the postal service, it’s expected that there will be international mail and therefore differences in writing styles. But also general differences since everyone’s handwriting is different. People and maschines need to be able to handle the differences.
I am from the US (Connecticut) and some people cross their “7s,” some don’t. I can’t remember what we learned in school. But I don’t remember our teachers Putting a huge pressure on us to write a certain way. As long as it was legible.
In comparison, I’ve had teachers correct my handwriting here in Germany since I sometimes write my upper-case “A’s” as large “a’s.” Kind of annoying since it’s just how I write…and since 28 years!
I’ve never crossed my sevens and haven’t seen anyone else do it either. I’ve worked a lot of places where numbers were written and 7 was always written as it appears typed. This makes me wonder if this is a regional thing in the states. But now that I know there could be potential confusion with overseas cards, I will definitely cross them when mailing internationally.
i’ve always learned to cross my 7’s and z’s as a default; and i used to slash my zero’s too, just in case, but i have grown out of that habit because there arent a lot of instances where O and 0 co-exist without it being obvious from the context. the only thing i can think of are serial/bar codes or alpha-numeric postal codes but postal codes usually have a standard letter-number-letter format that the slash matters less in that context 
i also wonder if, culturally, this is common among similar age groups and not just regionally - like writing/learning in cursive.
I think we are just overthinking. My address contain a street number with both 1 and 7, and I received cards with the numbers written in all possible ways. I have also received cards with an address written so badly I could hardly understand it - even if it was my own! - nevertheless they arrived anyway. The sorting machines have been programmed to recognize even very poorly written addresses. And if they really can’t do it automatically, humans can come to their aid. I think 1s and 7s written with or without leg is the least of their problems 
I have just started crossing my 7s all the time to avoid confusion (hopefully). Haven’t gotten the hang of adding a flag to a 1 though, every time I try I think it looks weird. Another one that I haven’t fully picked up, though I like the idea, is putting a diagonal slash through 0s to differentiate them from Os.
I’m always crossing 7. We were taught this at school
I cross the seven and the Z. I am born and raised in the US but was taught to do this by my European parents. I think it helps easily distinguish between 1, 7, 2, and Z.
Oh, yes, @adowning, I’ve seen the crossed Z sometimes. That makes sense with the 2. Thanks for sharing.
Popping this in the postbox today - not the way I was taught 7s, can’t remember how I was taught 1s.
About 8 years ago I went interrailing in Europe as a student and it was the first time I saw 1s written ‘like teepees’, and I honestly had no idea what it was!! However, now when I visit Germany, I love seeing the different way the number is formed.
Edit: also not the way I was taught 4s, or the way I should construct a 5 (was taught to put the ‘hat’ on last, rather than constructing all in one stroke)
This is so helpful! Thank you!!
It’s my first time to know crossed 7 when I started postcrossing. I once wrote a uncrossed version to Germany and German member told me the mail was misssent to other place. 
But I think the mail carriers in Taiwan are possible to tell 7 in both ways!
My postcode has also a 7 and I receive lots of cards with uncrossed ones without problems 
Actually, I also expect the address scanners of the various international postal companies to be able to recognise such differences - just as they should be able to read a wide variety of fonts and handwritings.
