Advice on ex-girl, new-girlfirend situation?

Alright my ex-girlfriend and I broke up back in November. It wasn’t a bad break up, and we were friends for about 4 months after the break up. I did all the usual stuff someone does when they’re hurting though. Called and emailed her trying to get her back. I ended up pushing her away. She stopped talking to me when she started seeing another guy about 4 months after we broke up. She dated him for about three months and then dumped him. I’m seeing someone now and I’m happy with her, but it bothered me how things got left between me and my ex, I don’t like being on bad terms with people, I'm on friendly terms with all my ex's it's something that's important to me. So I wrote my ex a letter apologizing for the main reasons we broke up (I had a little inside info) and for acting foolishly after the break up, and I told her that I would like to be on friendly terms with her. She wrote me on facebook and told me she forgives me, but that she couldn’t see us being friends without any issues, I didn't respond. The next day she emailed me again and said she had thought about it and we could try and be friends, and sent me a friend request. I told her that I was seeing someone, and that I couldn’t be friends with her on facebook. But that didn’t mean we couldn’t be on friendly terms. She didn’t respond then 2 days later blocked me. Either that made her angry or hurt her feelings, so I told her I wasn’t being mean. I was just being respectful of my girlfriend. My new girlfriend knows everything about the situation and doesn’t care if I talk to my ex occasionally. I explained to my new girlfriend that it bothered me how things got left between me and my ex and that I just wanted everything to be cool between me and my ex, my girlfriend is fine with that. A few days later my ex unblocked me and emailed me saying that my email account was sending her junk email (spam) at work. I told her I would look into it. I haven’t followed up with my ex on the junk email situation yet, and I don’t know if I should. I would like for my ex and I to be on friendly speaking terms, but I don’t know what my boundaries are as far as contacting her. My ex said we could try and be friends, and is obviously willing to speak to me again, but I don’t want to push the matter. I guess I’m just looking for some advice on how to handle the situation. Should I follow up with the junk mail situation? Since she’s speaking to me again how often would it be ok for me to be friendly to her? How can I assure her that I’m past everything and just want to be friends, so that she doesn’t think I’m going to pursue her anymore. Any helpful advice would be appreciated.