Helena Nelson at Happenstance (a Scottish publisher going since 2005) has some interesting things to say from behind the desk receiving tottering piles of poetry submissions,
In my stack of envelopes, there will be at least six or seven, and perhaps up to ten, from poets I have communicated with before. I will have invited some of them to send more poems, and the consequent familiarity will make those texts feel friendlier. However, the associated guilt will be greater if I can’t make any publication promises.
[…] For poets desperately keen to find a publisher, it may be worth noting that poetry publishers, once established, have a constant mental list of people they’d like to work with and publications they’d like to do. These arrive by one route or another, some of them through personal recommendation, or because one has met them or heard them read. The ‘window’ operated by a few of us is, effectively, an added extra. Most publishers start to say ‘no unsolicited submissions’ simply as a way of making the workload manageable. But they do get submissions, of course. There are other ways. There are always other ways.