Split your message into several parts if it is rejected because it is too large for the list. Alert subscribers to the existence of files you wish to share, and let them request copies from you privately. Anything about wild birds or birding in Texas, or anything legitimately related to these topics. For example, reports of invading species in New Mexico are obviously of interest to West Texas birders, and are appropriate to post. Never send a post to Texbirds with an attachment.
Attachments are how viruses are spread through email.
If you have a great picture of a Black Noddy you took at Padre Island that you want to share, send a post saying you have the photo and ask who would like it to respond to you privately. Then send it just to those who respond. Even better, place it on a web page, and include the URL in your posting. If you have information that you think might be appropriate to send out to the list, please check with the list owners first. Birding notes not related to Texas birds or birding.