Added the first mail error

ref #118

src/errors/MailErrors.ts

@@ -0,0 +1,12 @@
+import { IsString } from 'class-validator'
+
+/**
+ * Error to throw when a permission couldn't be found.
+ */
+export class MailServerConfigError extends Error {
+    @IsString()
+    name = "MailServerConfigError"
+
+    @IsString()
+    message = "The SMTP server you provided couldn't be reached!"
+}