feat: add mail/v2

mail/v2/docker/opendkim

@@ -0,0 +1,11 @@
+FROM alpine:3.15
+
+RUN sed -i 's/dl-cdn.alpinelinux.org/mirrors.ustc.edu.cn/g' /etc/apk/repositories  \
+    && apk add opendkim opendkim-utils \
+    && chown opendkim:opendkim -R /etc/opendkim/ \
+    && chmod -R 700 /etc/opendkim \
+    && rm -rf /var/cache/apk/* 
+
+EXPOSE 8891
+
+CMD ["/usr/sbin/opendkim", "-f"]