Why they use the mailbox? in EU everyone and his mother just use official forums or /world chat, since buying gold is allowed by Blizzard GMs:
GM confirming it is legal:
X__I have just confirmed with A GM that trading Retail Gold for Classic is allowed - #63 by Perl-anetheron
X___https://cdn.discordapp.com/attachments/728876914344853567/728876937967304724/uff2.png
Couple hundred Goldsellers in official forums, for months on end, no bans ever:
X__https://eu.forums.blizzard.com/de/wow/search?q=retail%20topic%3A69688
On Venoxis EU (biggest server) Edgemaster sells for 7 tokens, 140€, completely legal and like every other day in /world chat.