Multiple IMAP servers are supported by the config file. If more than one IMAP server is configured then a dropdown box will appear on the login page to select which IMAP server to login to. Here is the relevant portion of the hastymail2.conf file:

# ALTERNATE IMAP SERVER SETTINGS
# ------------------------------------------------------------------------
# Hastymail can support logging into multiple IMAP acccounts using the following
# settings. Each additional IMAP server will be displayed in a dropdown box on
# the login page. Additional IMAP servers should be defined with the "alt_n_"
# prefix where n is the number of the server. You can configure as many IMAP
# servers as you need this way by setting up "alt_1_" settings, then "alt_2_"
# settings etc. Any setting NOT defined for an alternate IMAP server will
# fallback to the default imap server setting.

#alt_1_imap_port = 993
#alt_1_imap_server = 127.0.0.1
#alt_1_imap_read_only = false
#alt_1_imap_ssl = true
#alt_1_imap_auth = false
#alt_1_imap_starttls = false
#alt_1_imap_folder_prefix =
#alt_1_imap_folder_exlude_hidden = false
#alt_1_imap_folder_delimiter_overrride = false
#alt_1_imap_use_folder_cache = true
#alt_1_imap_use_uid_cache = true
#alt_1_imap_use_header_cache = true
#alt_1_imap_display_name = Main (IMAPS)

Hope that helps,
Jason