Requires the library mod Collective.

Welcome Message is a server utility mod designed to make sending a welcome message to players logging into the server easy. There are three configurable messages which can be sent whenever someone joins the world. Each message can have a different colour and be completely clickable with an optional URL input. Any message config can also be left empty to prevent it from being sent.

By default the messages are only sent to players joining a dedicated server, e.g. not a singleplayer world. This can however be toggled in the config.

Configurable: ( how do I configure? )
onlyRunOnDedicatedServers (default = true): If the mod should only run on dedicated servers. When enabled it's not sent when in a singleplayer world.
sendEmptyLineBeforeFirstMessage (default = true): Whether an empty line should be send before to first message to separate the welcome from other chat messages that might be sent.

messageOneText (default = "Welcome to the server!"): The first message a player will receive when joining the world. Can be left empty.
messageOneColourIndex (default = 2, min 0, max 15): 0: black, 1: dark_blue, 2: dark_green, 3: dark_aqua, 4: dark_red, 5: dark_purple, 6: gold, 7: gray, 8: dark_gray, 9: blue, 10: green, 11: aqua, 12: red, 13: light_purple, 14: yellow, 15: white
messageOneOptionalURL (default = ""): If a link is entered here, the complete message will be clickable.

messageTwoText (default = "Downloaded from CurseForge! This is a clickable link."): The second message a player will receive when joining the world. Can be left empty.
messageTwoColourIndex (default = 14, min 0, max 15): 0: black, 1: dark_blue, 2: dark_green, 3: dark_aqua, 4: dark_red, 5: dark_purple, 6: gold, 7: gray, 8: dark_gray, 9: blue, 10: green, 11: aqua, 12: red, 13: light_purple, 14: yellow, 15: white
messageTwoOptionalURL (default = "https://curseforge.com/members/serilum/projects"): If a link is entered here, the complete message will be clickable.

messageThreeText (default = "You should probably edit this in the config :): The third message a player will receive when joining the world. Can be left empty.
messageThreeColourIndex (default = 15, min 0, max 15): 0: black, 1: dark_blue, 2: dark_green, 3: dark_aqua, 4: dark_red, 5: dark_purple, 6: gold, 7: gray, 8: dark_gray, 9: blue, 10: green, 11: aqua, 12: red, 13: light_purple, 14: yellow, 15: white
messageThreeOptionalURL (default = ""): If a link is entered here, the complete message will be clickable.

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You may freely use this mod in any modpack, as long as the download remains hosted within the CurseForge ecosystem.

Serilum.com contains an overview and more information on all mods available.

Comments are disabled as I'm unable to keep track of all the separate pages on each mod.
For issues, ideas, suggestions or anything else there is the Github repo. Thanks!