diff --git a/src/sbbs3/mailsrvr.c b/src/sbbs3/mailsrvr.c
index 431f557b0431b149ebf934ce70f3b5b068a63b57..86f7dc9919b8076f468cd9ed285bea1603cc79b2 100644
--- a/src/sbbs3/mailsrvr.c
+++ b/src/sbbs3/mailsrvr.c
@@ -5607,7 +5607,7 @@ static void sendmail_thread(void* arg)
 				} else {
 					server=p;
 					tp=strrchr(p,':');	/* non-standard SMTP port */
-					if(tp!=NULL) {
+					if(tp!=NULL && tp == strchr(p, ':')) { // Only one colon, not an IPv6 address
 						*tp=0;
 						port=atoi(tp+1);
 					}