FI and I are doing a super non-traditional TINY wedding in Spring (timed by some tree blooming) then having a giant picnic potluck party for the families/friends in July (when the weather is tolerable here). We've picked a date for the potluck party and I want to make sure our families know, even if it's far in advance (11 months). Note: out of towners won't be expected to bring food. Our local friends are compensating. Since this is such a non-traditional wedding-related event invitation I think e-mail is a perfectly reasonable plan. I'll make a pretty picture with clear text explaining that it isn't a wedding, it's a delayed reception, etc. Other than formality is there a reason not to use e-mail? Even our grandparents have e-mail accounts! It's an open invite to any family/friends and since we're renting out an entire giant park there will be plenty of space so I'm not worried about 'uninvited' people getting a copy.