I go back and forth with this. I have only done exclusive submissions with magazine articles, but with the length of time that most publishers seem to take now a days with rejections or the "no response" means no idea, I just wonder how any publisher, magazine or book, can expect we writers to NOT submit to multiple places? 225 days and finally a rejection? A few years ago I had sent a NF article directly to an editor who had published a different article of mine in the past. About a 9 months or a year later, I sent an email mentioning that I had assumed they were not interested in the article and I had plans on submitting it elsewhere when she quickly responded that it WAS under consideration and could I give them more time. And about 2 months later, they accepted it. . . but now that many magazines are doing "Submittable" I think the only option you have is to withdraw the submission. . .
I'm curious. If you state that it's a multiple submission, do you think that may push editors to respond quicker, or does it send the message that you, the writer, is not sure if it's the best fit so you're just sending it out and hoping something sticks? I realize poems are probably different than articles. . . but just wondering.
Good luck with your poem Maria!