Modifies https://code.google.com/p/prosody-modules/wiki/mod_offline_email and adds vCard email forwading.

mod_offline_email.lua

local jid_bare = require "util.jid".bare;
local jid_split = require "util.jid".split;
local os_time = os.time;
local t_concat = table.concat;
local smtp = require "socket.smtp";
local vcards = module:open_store("vcard");
local smtp_server = module:get_option_string("smtp_server", "localhost");
local smtp_user = module:get_option_string("smtp_username");
local smtp_pass = module:get_option_string("smtp_password");
local smtp_daemon = module:get_option_string("smtp_daemon");
local st = require "util.stanza";
local smtp_address = module:get_option("smtp_from") or ((smtp_user or "xmpp") .. "@" .. (smtp_server or module.host));

local queue_offline_emails = module:get_option("queue_offline_emails");
if queue_offline_emails == true then queue_offline_emails = 300; end

local send_message_as_email;

module:hook("message/offline/handle", function(event)
    local stanza = event.stanza;
    local text = stanza:get_child_text("body");
    if text then
        local username = jid_split(stanza.attr.to);
        module:log("info", "vCard  for %s", username);

        local email; -- nil by default
        local vCardRaw = vcards:get(username);
        if vCardRaw then
            -- note: it is not safe to do this in an open xmpp network
            local vcard = st.deserialize(vCardRaw);
            email = vcard:get_child("EMAIL");
            email = email and email:get_child_text("USERID");
            text = text .. "\n\n /to:" .. jid_bare(stanza.attr.to) .. "/from:" .. jid_bare(stanza.attr.from) .. "/";
            if email then
                return send_message_as_email(email, smtp_daemon, text);
            end
        end
    end
end, 1);

function send_message_as_email(address, from_address, message_text, subject)
    module:log("info", "Forwarding offline message to %s via email", address);
    local rcpt = "<" .. address .. ">";

    local mesgt = {
        headers = {
            to = address;
            subject = subject or ("Offline message from " .. jid_bare(from_address));
        };
        body = message_text;
    };

    local ok, err = smtp.send {
        from = smtp_address,
        rcpt = rcpt,
        source = smtp.message(mesgt),
        server = smtp_server,
        user = smtp_user,
        password = smtp_pass
    };

    if not ok then
        module:log("error", "Failed to deliver to %s: %s", tostring(address), tostring(err));
        return;
    end
    return true;
end

if queue_offline_emails then
    local queues = {};
    local real_send_message_as_email = send_message_as_email;
    function send_message_as_email(address, from_address, message_text)
        local pair_key = address .. "\0" .. from_address;
        local queue = queues[pair_key];
        if not queue then
            queue = { from = smtp_address, to = address, messages = {} };
            queues[pair_key] = queue;

            module:add_timer(queue_offline_emails + 5, function()
                module:log("info", "Checking on %s", from_address);
                local current_time = os_time();
                local diff = current_time - queue.last_message_time;
                if diff > queue_offline_emails then
                    module:log("info", "Enough silence, sending...");
                    real_send_message_as_email(address, from_address, t_concat(queue.messages, "\n"), "You have " .. #queue.messages .. " offline message" .. (#queue.messages == 1 and "" or "s") .. " from " .. from_address)
                else
                    module:log("info", "Next check in %d", queue_offline_emails - diff + 5);
                    return queue_offline_emails - diff + 5;
                end
            end);
        end

        queue.last_message_time = os_time();

        local messages = queue.messages;
        messages[#messages + 1] = message_text;
        return true;
    end
end

I'm using prosody trunk (version 0.10). Here is the error log:

@400000005610796f2f99823c jabber.tristank.de:offline_email          info    vCard  for guest
@400000005610796f2f998624 jabber.tristank.de:offline_email          info    Forwarding offline message to [email protected] via email
@400000005610796f2f99a564 c2s24297d0                                error   Traceback[c2s]: ...sody-modules/mod_offline_email/mod_offline_email.lua:48: attempt to concatenate a nil value
@400000005610796f2f99ad34 stack traceback:
@400000005610796f2f99ad34   ...sody-modules/mod_offline_email/mod_offline_email.lua:48: in function <...sody-modules/mod_offline_email/mod_offline_email.lua:41>
@400000005610796f2f99c4a4   (tail call): ?
@400000005610796f2f99c4a4   ...home/tristank/.toast/armed/lib/prosody/util/events.lua:73: in function <...home/tristank/.toast/armed/lib/prosody/util/events.lua:69>
@400000005610796f2f99c88c   (tail call): ?
@400000005610796f2f99cc74   (tail call): ?
@400000005610796f2f99cc74   ...cke/.toast/armed/lib/prosody/modules/mod_message.lua:53: in function <...cke/.toast/armed/lib/prosody/modules/mod_message.lua:18>
@400000005610796f2f99e3e4   (tail call): ?
@400000005610796f2f99e3e4   ...home/tristank/.toast/armed/lib/prosody/util/events.lua:73: in function <...home/tristank/.toast/armed/lib/prosody/util/events.lua:69>
@400000005610796f2f99e7cc   (tail call): ?
@400000005610796f2f99e7cc   ...ocke/.toast/armed/lib/prosody/core/stanza_router.lua:187: in function 'core_post_stanza'
@400000005610796f2f99ff3c   ...ocke/.toast/armed/lib/prosody/core/stanza_router.lua:135: in function 'core_process_stanza'