Nothing is ever going to supplant the need to read the magazine. Only by reading what they've already purchased and published will you know if your poems are right for them. And, to be perfectly frank, reading the published works of others will probably go a long way towards improving your own writing. Okay, this is our rule and has little to do with the publication industry. But it's just as important, probably more so, than any other rule we've given you to follow.
Editors buy poetry for a lot of different reasons.
They might buy a particular poem because it fits in with a theme they're publishing. They might buy it because it fits a page, or balances a layout. Unfortunately, the alternative is also true. The editor might return a perfectly good poem because it doesn't match a them they're publishing, because it's too long or short to fit in their next issue, or just because they've already spent their budget. Generally speaking, you cant' get a poem published unless it's good enough.